Thank you for the warm reaction to Part 1 of this analysis! The last part focused on all the myths I knew as a kid, this part will be characters from myths I haven't heard of or know little about, and those that have their origin based on literary or even historical sources. This part will be inspired by the Bilibili playlist by 野承Wild-Chase. His content is mostly Nine Sols analyses and memes (some Silksong as well), and this series is the one I mentioned in the last part where all the myths clicked for me. There are three videos in that series, one for the Sols, the Solarians, and the other characters. He even made English subtitles for most of his videos, so I recommend watching them yourself. Beyond it, I will use other sources to add to what he has already said, as I don't have as much personal input as the last part. I will add more cultural context and character analysis to compensate for it.

Note: I will refer to anything in real life using capital letters for each Chinese character and a space between each one, even if they already have English names that fuse all the syllabals; for the game character and terms, I will leave it as is to help distinguish them.

勾芒 (Gou Mang)

Gou Mang is the god of spring, east, the East Sea, wood (as an element of 五行 Wu Xing, lit. Five Phases/Elements. You can see it from the Chang Jie input guide in the last post as key C to G), and the Wood Star (Jupiter, the planet). He oversees life, can make people live longer and governs the growth of plants. He has the body of a bird and the face of a man (basically a harpy). He rides on two dragons to move around in Classic of Mountains and Seas. He works under Fu Xi (our Fuxi), and they rule over the easternmost part of the world where the sun rises. It is an endless forest with Fu Sang (扶桑, our Fusang) in the middle, and the perimeter is 12,000 Li.

Goumang comes from Yumin Kingdom (羽民, lit. feather people), a kingdom where food is scarce, so she works to make food more abundant using gene modification. She wears clothes that resemble a bird and even modified her legs into bird-like feet. A list of crops she made can be seen here in Red Candle Games' Discord, compiled by Einmera. It fits well with the Gou Mang governing crops with domain over spring and wood, and the mastery of gene modification as her rule over life. More on the control over life, the two Jiang Shi (僵屍, lit. stiff corpse, basically a zombie, they are so stiff they hop to move around) she has are called Shinue and Shiqiu (屍虐 屍窮 Shi Nüe and Shi Qiong, same shi as Jiang Shi; 虐 means abuse and 窮 means poor, I think Goumang names them after her trauma). They are probably referencing the two dragons Gou Mang rides on as she relies on them to fight Yi. The control collar has a design similar to the headband that was put on Monkey from Journey to the West. Tripitaka can recite a Tightening Spell, which tightens and causes a sharp headache to make Monkey stop. The control collar inverted this trope as the default is doing nothing, while the control bell issues commands to her Jiangshi. It represents Goumang's obsession with control.

奄老 (Yanlao)

This character isn't inspired by any myth. He is simply a stereotypical old man from the Yan Kingdom, literally. 奄 means the Yan Kingdom and 老 is old, basically an elder of Yan (I don't think he deserves "the" as the article). He has so little character that he doesn't really have a name. There isn't a lot to say about him except that he represents the older generation, where they talk about the virtues we should follow, and how the younger generation does not live up to those ideals, like not being respectful to the elders and such. It isn't surprising given his tenet is Legacy. Him scolding Yi for his actions by playing the wise mentor role is annoying, and we see him give up this benevolent elder act, this hypocrisy is even called out in the artbook. While he made some great points that Yi is being really selfish, and he is sacrificing all the Solarians on New Kunlun and even Penglai just to enact his revenge when they are still trying to develop the cure, he doesn't know the whole truth of Eigong's plan. His actions are ironically also dooming the entire Solarian race to become mutants, and there won't be a legacy left as they don't have sapience. I think we can grant him the title of "Boomer", Boomer Yan.

Despite him being pretty one-note, there are some inversions of this trope. We usually don't think of Boomers as tech-savvy. Of all the boss fights, his is the most technological as we fight the Sky Rending Claw, a giant mechanical claw and lasers controlled by him. We fight it by looking through the screen from his point of view, and his boss theme is the most electronic. I argue that it feels even more technological than Yingzhao. We know Boomer Yan is passionate about collecting relics and gadgets from the past, so it makes sense that he might have learned a thing or two about the science of the Turbulent era, as the Sky Rending System is from that era. Also, claw machines are extremely common in Asia.

截全 (Jiequan)

The Jie clan is inspired by the Jie Sect (截教) in the Investiture of the Gods (封神演義). They are opposed by Jiang Zi Ya's (姜子牙) Chan Sect (闡教, the same Chan as our Chan Kingdom). Investiture of the Gods is a romanticised telling of how Shang Dynasty (商朝, the same Shang as our Shang Kingdom) was toppled by King Wen and King Wu of Zhou with the help of Jiang Zi Ya as their military general and strategist. This history will be important and expanded on as we talked about Ji.

The Jie Sect has a lot of disciples and various ways to train, hence their method is regarded as unorthodox. It explains Jiequan's approach of getting stronger using gene modification and elixirs instead of training normally, and applauds Yi if he plays dirty by sabotaging him.

More can be said, but I will save it for Jietong and the world-building part in the future. A tease I will give is that Jie Kingdom seems to parallel Qin State (秦國) in real life.

莊周夢蝶 (Zhuang Zi's "The Butterfly Dream") + 胡天寶 (Hu Tian Bao)

Zhuang Zi (莊子, real name 莊周 Zhuang Zhou) dreamt that he was just a butterfly. As he wakes up, he is Zhuang Zi again. He ponders that if he is himself dreaming as the butterfly, or the butterfly is dreaming as him, as there isn't a way to distinguish between the dreaming and waking world.

This thought experiment is the basis of the Soulscape made by Lady Ethereal and her research team. And because the first versions are so vivid, when people stayed in for a long time, waking up from it makes them suffer from disillusion syndrome, where they couldn't distinguish real life from their dreams. As the Soulscape made dreams much more enjoyable than real life, waking up from it caused severe psychological distress, and exhibited self-harm, suicidal, and homicidal tendencies. Later, when Yi confronts Lady Ethereal, she questions what Yi believes reality and dream to be, and whether or not a distinction between them exists, the question Zhuang Zi asked.
One of the researchers, Xiaohe (小何), is her lover. (小 means small, here it is used as a prefix of affection before a name in Chinese. She also used it for Yi, calling him 小羿 as an affectionate and playful nickname, as he is smol) With this, we move to another myth that relates to her being gay.

An imperial inspector (tasked with travelling around the Kingdom to check on provincial officials) was sent to Fujian (福建). Hu Tian Bao fell in love with him because of how beautiful he is, and stalked him every time he started official duties. The inspector noticed but got scared, so he didn't ask why. Even after he moved on to other provinces, Hu Tian Bao followed him there. One day, as he was going to the toilet, he spotted Hu Tian Bao peeking at his ass (I didn't exaggerate anything here). When finally he asked Hu Tian Bao why he did it, he said, "You are too handsome, it's unforgettable. I don't know what pushed me to be this shameful." This made the inspector extremely mad, and he sentenced him to death by beating (being hit by clubs as you lie down on your stomach until you are dead). A month later, Hu Tian Bao's spirit sent a message to his relatives through their dreams¹, and let them relay it to the inspector, saying "My actions were offensive, and I deserved to die. However, because the reason for my death is me blinded by love, the underworld's bureaucrats² laughed their asses off (sorry) but were sympathetic. So they appointed me as 兔兒神 (Tu'Er Shen, the Rabbit God, with rabbit being a euphemism of same-sex relationship, not god of actual rabbits), the deity of same-sex relationships. Please build a temple so people can worship me." This is an actual religion started in Fujian in the 17th century with temples built, and it spread to Taiwan. After being suppressed as a cult during the Qing Dynasty, a temple to this god was built in Taiwan in 2006. Have you been so gay that you get exalted as the god of same-sex relationships?

You might be asking how this is related to Lady Ethereal, her name in Chinese is 蚨蝶 (Fu Die, butterfly³, but basically obsolete as we use 蝴蝶 Hu Die instead, so the choice is intentional), and Hu Tian Bao has another title, 蚨蝶母 (Mother of Fu Die, described as a goddess of lewdness), pretty much confirming she is gay as hell. The relation to butterflies might be why Mystic Nymph got involved.

¹ This is a common way for spirits to send a message to the living in China. You may see a parallel with Lady Ethereal's mastery of dreams, or how Yi accidentally came into contact with what's left of her in the game. Basically, her mind (or poetically, her spirit) invaded Yi's consciousness even if he is already awake and pulled him into her Soulscape, so she can offload her grief and guilt to Yi to punish him just as she punished herself, as she partly blamed him for going ahead with the Eternal Cauldron Project and forcing her hand to rush the Soulscape system.
² Those who determine one's afterlife based on their deeds in life, like dishing out punishments based on their sins or if they are allowed to go to heaven. You might be slightly familiar with it if you know Monkey's origin story from Journey to the West, where he gained a layer of immortality by removing his name, along with all the names of his monkey empire from the record so they can't die.
³ Butterfly represents psyche in Greek myth, and souls in both Greek and Japanese myths, but I didn't find a strong link in Chinese myth. However, it isn't that big of a leap even for people who have never heard of that connection before. Lady Ethereal's butterfly imagery, her work on Soulscape, and her mental anguish fit both the themes of psyche and soul.

Fun fact: Xiaohe and the other seven Soulscape researchers are stated to be based on the Eight Immortals by the artbook. The Eight Immortals obtained their immortality in different ways. They were all common people before and have their own flaws, hence they are relatable and well-liked. They are figures of worship in Taoism and live in Mount Peng Lai (蓬萊山, our Penglai, the Solarian's planet). They each have their own vessel they can channel power into. Each Immortal represents an aspect of human life: man and woman, old and young, poor and rich, lowly and noble. Xiaohe is based on 何仙姑 (He Xian Gu, the same 何 is used), and represents woman (the only one of the Immortals), and she has a lotus as her vessel. Beyond Xiaohe, I want to highlight a few other Immortals/researchers:

• Looking at the research team, you can see one of them has a long beard and eyebrows, and one is a lot shorter than everyone else, they might represent the old and young Immortals.
• If you pay attention to the researchers, besides Xiaohe, one of them is rather feminine as they have longer eyelashes and breasts, didn't I say He Xian Gu is the only woman in the group? Well, one of the Immortals, 藍采和's (Lan Cai He, the poor one) gender is ambiguous. For me, their name seems feminine. Depictions of them can be a man, woman, feminine man, appear/dressing up as different genders, and more. Applying our modern understanding of gender to a rather old myth is probably not productive, but I like to think they are genderfluid.
• Another Immortal I want to highlight is 李鐵拐 (Li Tie Guai, lit. "Iron Crutch Li", the lowly one), as his name suggests, he uses a crutch. There doesn't seem to be a researcher who directly corresponds to him.
• Finally, the Immortal 呂洞賓 (Lü Dong Bin, the man), we will talk about him more when we talk about the Three Great Sages. For the sake of the story, the researchers and the Three Great Sages have no relation, just that Lü Dong Bin is used in a different context as he is layered.

There is a saying 八仙過海，各顯神通, (lit. The Eight Immortals cross the sea, each revealing their divine power). It's from the myth that each immortal uses their own vessel to cross the sea in their own way. It means that everyone achieves the same goal in a unique way, expressing their individuality (which is a bit rare for the Chinese society as we are more collective). It also means people showing off their skills and expertise, working together to achieve a common goal. As I said, all of their stories are pretty inspiring (dare I say, woke), especially for common people. They are well-liked for a good reason. (There's more to this story. The Dragon King of the East Sea got annoyed and kidnapped Lan Cai He. The Immortals went to war with him. Even as the Dragon King called for the other three to help, they still almost lost. Until Guanyin had to step in and create a truce. The Eight Immortals are pretty powerful, but it isn't too important for this analysis.)

姬昌 (Ji Chang)

Ji Chang is a ruler of the Zhou state in ancient China (Ji is his surname, Zhou is his sub-surname). Ji Chang laid the groundwork for his son to overthrow the Shang Dynasty as an official, as he died before the war to topple it. He also wrote I Ching (易經, Classic of Changes, sometimes called 周易 Zhou Yi after the dynasty), which includes a system of hexagrams used for divination. Ji being able to divine using hexagrams so proficiently is because the person he is based on wrote it. His Celestial Sphere projects the cosmic and constellations during divination, the relative positions of the planets to the stars are often used to determine the results of a divination as well, but it's a separate divination system from I Ching.

Ji Chang has been posthumously honoured as the founder of Zhou Dynasty and titled 周文王 (Zhou Wen Wang, lit. Civil/Literary King of Zhou) because of his good governance and having written a book. This might be why Ji picked up being a historian, and the couple of people we saw writing, besides Shunashuan.
By the way, all these King/Emperor [noun/adjective] of [dynasty] titles are posthumously given, like his son is later titled 周武王 (Zhou Wu Wang, lit. Military/Martial King of Zhou) because he won the war, and 文武 is often paired together as a noun for the different sides of government. In modern terms, the politicians and the generals. Sometimes, there are shades thrown at tyrants or pushovers, like 哀帝 (Ai Di, Sorrow Emperor), there are multiple of them in different dynasties, and they all died quite fast, some ended their dynasty.

Ji is based on the person supported by Jiang Zi Ya, as stated earlier in Jiequan's section. Jiang Zi Ya is enemies with the Jie Sect in fiction, and our Jie clan is based on them. We can form a correlation between them and expect Ji to have been an enemy to the Jies at some point. Despite Ji being the seer¹ and a friend of Jietong, he is the ferryman who carried Lear away, leading to the Jie Kingdom's downfall. I didn't really buy it at first until this connection added a bit more fuel to it, and then I saw the comic lecture document confirming it.

As the last post said, the Yellow Emperor took the surname 姬 (Ji) from a river. While Yellow Emperor is a myth, 姬 is one of the earliest surnames in the history of China, along with 妊, 姬, 姜 (Yan Emperor's surname), 姒, 嬴, 妘, 媯, 姚, 姞. The radical 女 (woman) exists in all of them, it suggests that early Chinese society was matriarchal. For the word 姬 itself, it has multiple meanings: it is used for a beautiful person (usually a woman), a concubine, a princess (mostly used as a Japanese kanji nowadays), or the title of a woman official during the Han Dynasty (used like [name] Ji). As you can see, the word is archaic and isn't used in modern times anymore, relating to Ji's ancient nature; its meanings are rather feminine even for a word already having the 女 radical. This might explain why Ji looks androgynous despite using he/him pronouns. While we don't know much about the ancient society of Penglai, if it mirrors ancient China's, he could have a bias that womanhood is more important. While I am at it, I want to inject a bit of modern understanding into Ji. If I were to live for thousands of years, I probably would have experienced most of the things the world can offer, including all types of relationships. At that point, I think strict gender roles might not be that big of a priority, nor caring about what I wear would offend others, which leads us to...

His costume seems to be inspired by Buddhist clothes, mainly Tripitaka's as there are a lot of media representations of him. The headgear having a strip of fabric attached from the sides is a feature of the Five-Buddha Crown (五佛冠), but the Fez-like hat itself with an eye is original. His clothes might be a kasaya that Buddhist monks would wear with a lot of liberty taken (but not just exposing the right shoulder), and also a bit of Qi Pao (旗袍) with the side of his legs exposed (well, pretty much all of it). His cape/veil is red and has some gold lining, similar to the Zu Yi (祖衣, monastic robe), and the hexagonal gold lining on it resembles the Five-Buddha Crown stated by the artbook. He has a staff that acts as a spear and resembles a khakkhara without the rings. Both the staff and robe are the gifts Buddha gave to Tripitaka if he is willing to embark on the journey. Also, most media representations of Tripitaka look androgynous, which might have inspired how Ji looks as well. (I heard that Ji was meant to be non-binary until it got changed. I am not surpeised give his story and design, but I haven't seen the actual source of this claim.)

He has lived for thousands of years, but he said he passively lets history flow and usually does not interfere before we battle him. Like him witnessing the suicide of Jietong, the Inaction Declaration, Lear's "death" by being absorbed into the Fusang to the Limitless Realm, and simply recording all of history in the Grotto of Scriptures.
However, he isn't completely detached from reality either. He is at least friends with both Jietong and Lear, probably considers Yi one too with his determination and power to make big changes to history, and there are definitely more people he has cared about. He is the seer of the Jie Kingdom and remains so for the Jie clan even after they are removed from power, as Jiequan still calls him by this title as a descendant. His conversation with Jiequan isn't simply telling him he will die because of his divination, he talked about the legacy of the Jies and is concerned about what he is doing to his body. He ferryed Lear away when he and his family were chased by Jietong, and became his deputy captain of the Fangshi Guild's elite guard (this title might be the most sentimental one for him, as he announced it when Yi fights him). He recognises moves used by Lear from Yi, and likely promised Lear to protect the Grotto. He hung onto mementos of sounds, images, and texts other than the history he recorded so he could remember the important people and experiences. His longing for connections and fear of loneliness (which he already feels constantly because of his immortality and inevitability of losing people he cared about) made him board New Kunlun, because he can't die from Tianhuo and there won't be any Solarians left on Penglai.

For why he is so passive, I think it is because his divinations are too accurate, so he can always see the outcome. Whatever he does won't change it, so he only acts when he knows he plays a part in it. I don't know how much agency he feels he has, but as he said, his existence is a curse and he doesn't have much free will. With his divination, he knows the result, but not the reason. I think this is something he takes solace in because he can still form genuine connections with other people. When he divines for Yi one last time, he is shocked by a divergence in the results as it rarely happens. This refers to the two different endings we can get.

¹ Seer as a title evokes that he is just an oracle for the Jie Kingdom (and later the Jie clan), but it is more than that. In Chinese, he is referred to as 國師 (Guo Shi, lit. teacher of the kingdom). It is a title given to a religious person who is virtuous and knowledgeable, which fits his character perfectly (him being worshipped even as a kid, having thousands of years of life experience, and the ability to divine). It being condensed into just seer doesn't fully encapsulate the importance of his role, but it's hard to translate directly so it highlights the most important aspect. With him being a "teacher" of sorts for the Jies and his concern for Jiequan, Ji might have helped raise him given their familiarity. As for why Jiequan still went down the wrong path, maybe Ji divined his tragic end, so he only does so when Fate makes them cross paths. Them not being as emotionally close as they can be probably made Jiequan's descent into darkness worse.

易公 (Eigong)

Eigong's design resembles the depiction of Queen Mother of the West (西王母) in Classic of Mountains and Seas. She is one of the earliest woman deity. Queen Mother of the East and her are the sun and moon goddesses respectively, who govern the sunrise and sunset. It's obvious which one is which based on their cardinal direction. Some also say they are the goddesses that rules over life and death respectively.
Queen Mother of the West in Classic of Mountains and Seas is also in charge of natural disasters and diseases. If you have seen the last part, you might be connecting some dots. There are already some inversions: she is the leader of the Sols, not the moon; she seeks immortality, as opposed to being in charge of death (but she also doomed everyone); she wanted to cure Tianhuo when Queen Mother of the West is the plague goddess... well, Eigong also made it, and it wasn't a natural disaster at all.

As the story of Chang'E Flying to the Moon goes, she is the one who offered Hou Yi immortality vials. However, the story inverts this plot as Eigong isn't the one who gave Yi his immortality, and she does not have access to immortality from peaches. (Speaking of peaches, here is just a random theory. The growth of mutated Tianhuo from Ji's gene and the mutants being pink might be inspired by peaches, and she views it as her actual solution for immortality for the species. But this evidence is paper thin, and the flower of Tianhuo looks more like a lotus.)

I mentioned her name has the same character as I Ching is one of the connections I made myself. While this is true, there is no direct connection I can see besides Taoism in general. If I stretch the word, 易 is used in easy (容易), which is the opposite of her boss fight. 易 also means changes, it might refer to the many deceptions and the change in stance when she discovered mutants? Not very convincing, I know.

軒轅 (Xuan Yuan)

Shuanshuan (軒軒) is just a nickname by affectionately doubling the first character. His real name can be seen in-game, and is the same as the Yellow Emperor's, 軒轅 (Xuan Yuan, the pinyin is different from his English translation, probably because Sh- is easier to read/pronounce for English speakers), one version of his sub-surname is You Xiong (有熊¹), and his surname is Ji (姬). There is a character 猿 (Yuan) that is similar to the second character in his name, meaning ape. It has the radical 犭 instead of 車, usually used for Chinese characters for animals or beastial nouns or verbs (車 means cart/car, 轅 means axle/shaft). 猿人 can be translated as hominid or even a name for Homo erectus, it means ape man when translated literally, hence why humans are called Apeman in this universe.

The Yellow Emperor is one of the Three Sovereigns, and is considered the most important one as he is the origin of the concept of China, and his descendant founded the (likely fictional) Xia Dynasty. He is said to have invented cooking, housing, calendar, and funeral rites. He asked his official to monitor the sun, moon, and planets, and to create written language (our friend Chang Jie from the last part), math, musical scale, the Sexagenary cycle (combining Heavenly Stems and Earthly Branch²), percussive instruments, picture, mortar and pestle, bow and arrow, and boat. His wife domesticated silkworms, invented weaving, and created clothing; another wife invented the mirror. Even if the Yellow Emperor were a real person, all these attributions are fictional. However, in Nine Sols' universe, we know our Shuanshuan is very clever, picking up skills like playing the flute, drawing, writing in Solarian, and even programming with ease (music, picture, writing system, and something similar to math). He also has people like Yi and Kuafu who help him learn about the world with way more advanced technologies. It explains why he is credited with creating so many things with a lasting impact on the civilisation after the Apeman returned to Pale Blue Planet.

¹ From the Yellow Emperor's dad (son of Nü Wa and Fu Xi) being the leader of You Xiong area, 有熊 means "has bear". This caused some fans to jokingly suggest the "bear" is Kuafu because he looks like one.
² Earthly Branches consist of 12 characters 子丑寅卯辰巳午未申酉戌亥, it is most commonly used in combo with the 12 Chinese Zodiacs, and splitting a day into 12 時辰 (Shi Chen), each one lasting two hours. It is combined with the Heavenly Stems (the ordinal numbers) together, making 60 unique combos (their lowest common multiple), and why it is called Sexagenary cycle (sexa- is a prefix for "six", and "gen" from ginta for "ten", and -nary, similar to binary, meaning "consisting of" as a counting system). As always, it is used for divination, even in modern day, like this year (2026) being the Fire Horse (the ten Heavenly Stems are divided by two, cycling the Five Elements twice) and how it affects certain people's fortune.

Ending Thought

This is another big one, and it covered all of the Sols and most of the prominent characters that appeared in the main story (sorry, Chiyou and Lear). Next time, I will cover every notable character whose stories happened in the background or other media, a tease will be posted in the comments.

I just became a fan recently, so I didn't participate in The Turbulent Era event. I don't know if there are more characters and lore I missed, nor have I seen anything from it documented, as Red Candle Games' video on it doesn't really explain in detail what people have to do or the lore they discovered. If you can, tell me where I can find more about it.

A parting (not really) trivia for Yi and Heng's relationship

First thing before I dive deeper into this topic, we know incest is immoral, not everyone here ships them, and people who ship them do not condone it happening in real life (I hope). This section will be a reiteration of another 野承Wild-Chase's video on it, with me adding a bit more to it. My version isn't original and the video has English subtitles, so give it a watch first. What I will say is just an analysis of the two characters' words and actions, and how they reflect their relationship from some people's perspective. This is also a fictional depiction of such a relationship. Please don't harass people who ship them or Red Candle Games for making it ambiguous.

Hou Yi and Chang'E are a married couple, even as the developers changed the dynamic to highlight a different type of relationship, they chose this pair of characters as a basis for a reason. At the very least, Heng is someone important to Yi. Of course, the character based on the myth doesn't have to be one-to-one, a lot of them even invert parts of their origin (including Yi and Heng's). Being siblings and important to each other doesn't mean they love each other, but...

Comparing Yi's reaction to his parents and Heng's refusal to board New Kunlun, Yi didn't understand his parents but ultimately didn't care, unlike how emotional he got with Heng. Yi and his parents never had a good relationship because of how they viewed science, it isn't surprising that Yi doesn't care about them. However, despite Heng always having a similar Taoist view to accept whatever may come, she is met with a lot of resistance by Yi when she refuses. Heng is curious and is always there for Yi when they are younger, unlike their parents. In turn, Yi cared for her so much that he considered her a part of himself, her suffering felt like it would reflect back to him, like he didn't do enough to protect her. This defensive instinct usually comes from two sources: parents for their children and partners who care deeply for each other. In his mind, there is never an option of "living without Heng", he might have taken extreme measures to bring her to New Kunlun if he hadn't died by Eigong's hand.

Heng expresses her feelings for Yi in subtle ways that can be seen as just care from family. Every message is rather normal as she talks about things happening to and around her, and how she misses him. Yi and the Tiandao Council have sacrificed a lot to complete the Eternal Cauldron Project, and will sacrifice more as they reach Pale Blue Planet, something I am sure Heng disagrees with. Heng already saw the length Yi went to when creating Mystic Nymph, that he would even give up his life for it (even though it is to protect her from his own mistake), and how he couldn't be reasoned with when she knew the roots were suffocating, because he couldn't have known and wouldn't believe her. Heng knows everyone will return to the Tao, she may have a hunch that Yi's plan to cure the Solarians and extend the species survival is a doomed effort. However, she still couldn't convince Yi to stay with her on Penglai, just as she couldn't stop him from the explosion incident that had already killed him once. She didn't force him to stay with her and still wished him the best with her messages lightyears away, but she won't know he will die again soon and be out of action for a long time. Just as Yi failing to convince her to board New Kunlun hurt him, she feels the same pain from not having done enough to prevent him from going away, and unknowingly failed to protect him from death both times.

In the message about her wound that couldn't be closed because of Tianhuo, she wished and begged Yi to come back, even if it was just for a second. This is one of the few times she isn't subtle with her feelings for Yi. The other time, she said she wanted to spend the rest of her days with Yi, and he is all she has left. Heng can likely find a partner and not be alone anymore if she wants to, but she didn't. It showed us that Yi is irreplaceable for her. In her last message, she said "If you have a new family, will you still remember me?" This line feels very intimate, like a blessing written by a lover who won't meet again, wishing him luck in finding someone else. It's almost as if Heng wanted to be with Yi forever, but couldn't say more as it would be too much even for her, so she replaced "lover" with "family". As you may have already felt, each of her words and feelings is also carved into the heart of Yi.

For some indirect evidence, the devs didn't really erase the incestuous relationship between Nuwa and Fuxi. They could have done what Hades did to make the family tree branch out more to remove most traces of incest, which means this theme isn't off the table and can be intentional.

With all the dialogues pointing towards them being in love, why did the devs still make them siblings when they are already a couple in the original myth? Well, this might be intentional. Yi isn't good with feelings, he is blunt but isn't straightforward. He refuses that Heng will one day leave him (especially when he became immortal and Heng still ages, on top of everyone contracting Tiaohuo). It would already be hard for him to confess his feelings for Heng even if they weren't blood related, so the devs made them siblings to make it impossible. Yi rationalised his feelings into doing so for his family (even if he is not on good terms with his parents) and to cure Tianhuo. If he can focus on the cure to save the world, he can avoid accepting Heng's death (if it happens) while masking his feelings as familial. A bonus if the cure is made, he can extend the time with her. Questions like "why do you want her to board New Kunlun?", "why her decision to stay on Penglai made you hurt?", and "why do you want to be with her forever?" would have been really hard to answer for Yi because they are siblings.
For Heng, she has always been more open with how she feels, even if it is subtle (the opposite of Yi). If it weren't for the taboo, Heng might have confessed her love first, making Yi rethink what he is doing and why, and may come to an epiphany about Tao with Heng and abandon the project. If there are no internal conflicts for Yi to overcome, where would the story go? (Here, Wild-Chase used a story beat of Attack on Titan as an example that parallels the relationship of Yi and Heng. It's a great comparison, but I have never watched AoT, only learnt some details through osmosis, so I won't go into details as I don't have a perspective).
This taboo set up a barrier that both Yi and Heng cannot pass, allowing the story of Nine Sols to be possible. Even with it, they still love each other in their own way: Yi doing what he thinks is best for Heng; Heng stands firmly by Yi even with their different views. Besides the final confrontation, Heng never argued with Yi, she was willing to take some frankly vile insults and still did not resent him. As long as Yi pursues things he wants and is happy, she will support him. Heng refuses to board New Kunlun not only because it is unnatural and against the Tao, the cryosleep only slows down Tianhuo's advancement. It would take away precious time she could have spent with Yi if they had just stayed on Penglai, where they could recall every memory on the planet they are familiar with together. Instead, in her last message, she recalled every detail of Yi alone when she was about to pass away, knowing he couldn't reply to her.

For me, I don't ship them. I understand why people ship them, especially for people who have an understanding of the mythological origin. But, I genuinely cannot picture them being romantically involved despite the canonically deep bond, unlike other ships I like, even in this game alone, that require way more headcanon to work. I can be convinced the right word for their relationship is "soulmates", not in a sense that is romantic or god forbbid, sexual, as they have such a deep relationship that truly goes beyond siblings, yet the circumstances and different viewpoints separate them in the end. Only after a journey full of self-reflection did Yi understand Heng's viewpoint, after she had been dead for 500 years and they are 500 lightyears apart where they have no chance to see each other again. Yet, they still met each other on the Tao a moment before Yi destroys New Kunlun and himself for good, allowing them to reunite at last, as souls.

If this relationship is how the story is intended by the devs while keeping it quiet, it might be one of the best uses of incest in fiction, when most other times it just boils down to shock value. I can say even the Fengs' relationship is mostly for shock, even if they have an ironclad mythological basis for it. I can see Nuwa have a carnal desire for her brother, but if Yi and Heng were to have feelings for each other, their desires always felt exclusively emotional.

Someone in the comments of Wild-Chase's video said, "If you tell them to marry each other, they will be shocked; if you tell them to be together, love and respect each other from now on, never leave or forsake and be forever faithful, for better for worse, for richer for poorer, in sickness and in health, ever supporting, ever protecting, sharing weal and woe, till death you do part (just a wedding vow), they will claim they planned on doing that already."
Another comment pointed out that Heng is the reason Fusang can revive Yi. In some way, she is still always there by Yi's side even after she is gone. (On top of all the messages she sent to Yi, and the memories with her from all the flashbacks. Yi is reminiscing about every detail of them together by himself as well.)

One last disclaimer, having incest in a story is not an endorsement by the devs, it can be used as a storytelling device just as any other taboo themes people can utilise. Most people here already know some indications of Yi and Heng's relationship might be deeper than siblings for long enough, and Nuwa and Fuxi already took most of the heat, so I hope I won't start a riot against Wild-Chase, any shippers, or the devs, like the dev of The Coffin of Andy and Leyley still got harassed off the internet even when incest is depicted as bad.

Links to other parts

Part 1: https://www.reddit.com/r/NineSols/comments/1ste7f9/nine_sols_mythological_inspiration_from_the/