Sukuna is NOT a "Force of nature/ one-dimensional evil for the sake of it" villain that a startling majority of fans/dissidents of JJK's writing seem to misunderstand about him. He's not even a Hedonist.
One of main themes of JJK that Yuji eventually realises in chapter 265 is that humans are neither inherently good or evil, they can be bound to either roles depending on their circumstances. While people tend to focus on Yuji's aspect of development, where he grows out of his cog mentality and accepts his value as a person outside of his ability to fulfil his role, Sukuna's character in this theme is often heavily overlooked.
Throughout the story, Sukuna is often displayed as this otherworldly, hedonistic force of nature villain that tramples over anything that stands in his way. Classic examples of this include Uro's description of him after her fight with Yuta, his initial actions in the Shibuya, after first incarnating etc.
Yet, as we continue throughout Shinjuku Showdown, there are blatant signs of Sukuna being far more human than what is initially portrayed, what he wishes to portray to others.
Case in point, his conversations with Yuji and Kashimo. When Kashimo asks him if he's satisfied, why he decided to split his soul to become a cursed object, Sukuna explicitly dodges his question, changing the topic to talk about love and why he doesn't need to satisfy him, its pretty clear he wasn't. Sukuna's actions simply don't match that of the hedonistic individual he's initially shown to be, hedonism is all about maximising pleasure, enjoyment.
Yet, Sukuna simply kills and eats out out of boredom, to pass time until his death. His actions match that of a nihilist, he finds no greater meaning in life other than objective, in-the-moment metrics. This trait is further explored in chapter 265, Sukuna places his fish above Yuji's in value simply because its bigger, while Yuji retorts, saying his fish is more rare. Rarity is a subjective, personal value that society created, something Sukuna cannot understand, due to his circumstances as a starving child, treated as a outcast by his family. He has never known true human connection, and as a result, finds no meaning beyond objective metrics like strength, which is why he seems to value it so much, not because he is obsessed with it, but because it simply exists, theres nothing subjective about it (in his view). Sukuna is also objectively shown to be a genius, he discusses haiku with Yorozu, he has knowledge of flowers, and yet for all his smarts and knowledge, he's unable to understand something fundamental for others.
After his death, we this expanded as well, out of fear of being immolated by his own curse of being abandoned by his family after eating his twin from starvation ( a very human emotion", Sukuna resorted to spewing out his own curses, to portray this outward image of being a enigmatic force of nature. And yet, Sukuna himself is aware of his own emptiness, his life's lack of meaning. When talking to Kashimo and Yuji, he's actively trying to listen to them, but he simply can't understand them.
It only makes Yuji's pity at the end so much more staggering. When no one else in the story, even the "strongest"s, Gojo and Kashimo could understand Sukuna, it was Yuji who eventually realised just how pitifull, sad and empty Sukuna was. Nothing more than a human who could find no personal/subjective meaning in things, a empty shell born of the unfortunate circumstances of his birth, who desperately tried to hide said emptiness by being the "strongest", by being a "curse".
Right before he dies, Sukuna explicitly calls himself a "curse" because as long as he lives, he could do no more than hide himself behind a lie, a false persona.
This was done a whim, prob could have expanded on it more but can't think of anything else for now