I've been playing HI3 since the early days and this Seele is one of the reasons why I'm still sticking around ever since Mihoyo got mainstream and character quality has somewhat dropped off. One of the biggest things I look for in a game is character development, which is why I like Kiana, Mei, Fu Hua, Bronya, Seele, and "Seele" and how chapters will focus on their journey. Kind of hard to do when most games nowadays just have a silent/self-insert protagonist.
Our current part 2 Seele is what happens when she's reunited with supportive family and friends if GGZ and what little I know of hsr is anything to go by. GGZ Seele suffers a worse fate of never being able to rejoin Bronya in reality due to reality rejecting her and "Seele" taking control of her body to fight the main trio under a misunderstanding that could have been prevented. Seele ends up sinking even deeper into the quantum sea where the most she could do was to enter Bronya's dream and create a story for the two of them. Obviously all dreams end, but long story short, to save Seele from just dissapating, Seele and "Seele" personalities fused, which ends up to be somewhat similar to hsr Seele's personality.
So in HI3, Seele starts off as basically a timid cry baby who is scared of violence. Seele depended on her other self's power many times when she was alone, though she's terrified of her other self that doesn't actually have a name until chapter XXIII where I think is the turning point for their relationship. Seele was finally reunited with her family (Bronya and the twins) and was making friends (getting to know Kiana). Seele begins combat training, trying to get stronger and was making active steps to trying to get to know more about her other self, but "Seele" was insecure with the belief of how she was no longer needed. It wasn't until meeting the herrscher of domination that Seele let's her other self know that after all this time, she trusts her 100%, letting her completely take over Seele's body to take care of the threat. It wasn't until after HoD that they finally sit down in their mental mindscape that her other self picks out the name "Seele" for herself, showing their unique bond.
Part 1.5 flips the dynamic when they are separated from each other. It brings the idea that perhaps "Seele" was more dependent on Seele than she initially thought. Seele on the other hand, has developed to be much stronger than we have thought, being able to pull off a self-sacrifice (maybe Kiana was rubbing off on her).
Part 2, from what little we have seen of Seele, is now the one somewhat controlling the relationship, as seen with her nagging Bronya about overworking and even getting Bronya, Coralie, and Helia to be scared of pissing off Seele. This is the only iteration of Seele that we get to see actually grow up. She went from a timid crybaby to someone that others rely on. Aside from Kiana's character development, I think this Seele's journey is Mihoyo's most well written story. Anyways, I'm excited to see what "Seele" has been up to in Part 2.