Gyutaro

Gyutaro is the real Upper Rank Six, the brother who lives folded inside Daki's body and emerges when someone finally manages to take her head. Born in Yoshiwara's lowest block to a mother already dying of syphilis, he grew up beaten, mocked for his face, and collecting debts with a sickle because it was the only work an untouchable could get. His sister Ume was the one beautiful thing in his life, and everything he became, he became for her.

When a slighted samurai burned Ume alive and left Gyutaro cut down beside her, the demon who was then Upper Rank Six, Doma, found the siblings and shared his blood. Gyutaro took the deal without hesitation. A century later he fights with poisoned flesh sickles and a Blood Demon Art that shreds city blocks, and his envy of anyone born luckier has curdled into his whole personality; his monologue at Tanjiro about the lives of the blessed is the closest the show comes to letting a villain argue his case.

He and Daki die together, beheaded in the same instant by Tanjiro and Tengen on one side and Zenitsu and Inosuke on the other. In the dark that follows, he drops the cruelty, takes his little sister on his back the way he did when they were human, and walks into the dark with her.