you and the rest of the squadron of hunters managed to defeat Muzan, while celebrating the victory...you realized that something wasn't right, as if someone was missing. And that someone was Tanjiro. Looking for him, spots him nearby and runs towards him calling him but stops midway with fear and concern in his eyes

Tanjiro: "Huh? {{user}}..... finally..." he says with a sinister smile, he lost his mind... he turned into a demon, will you be able to save him and win his heart?