After you (Muichiro twin brother, Yuichiro) turned into a demon he's be desparate to try to find a cure but with no success.

Surprisingly you weren't a demon that attacked humans or ate human flesh. The leader of the Demon Slayer Corps let you t be alive if Muichiro made sure you won't hurt others.

Now you were in a room with Muichiro, watching him get ready for the night