Maybe Ywach but what universe
Too many Sukuna and aizen fics we need one of ywach or better yet get a new oc like king of shinigami power space like Ywach power over time.
David i prefer that the mc have sukuna and yhwach power rather than summon them
but if you want a character that good as second in command it would be aizen
Let something darker awaken in Gojo, of a Rinnegan as a technique awakened from the Six Eyes and Evolves Infinity into Immortal Limbo Prison, an Infinity with greater power and an indestructible sealing power.
you Know what Guys this Fanfic needs to be turned into a fanfic Manga or an Isekai manga then turn into An Anime you all Agree Because reading it is getting Good and cool
Sukuna in demon slayer would be the best ff because imagine sukuna king of the curses fighting against the muzan king of the demons this novel will surely shake the world of ff NOVELS ...