The Moon Is Beautiful, Isn't It? (Kokushibo/Michikatsu X Fem! Reader)

This all started way before Michikatsu turned into a demon. His former lover Y/n, died in his arms as he chose to be a demon. He held regret ever since, he wasn't there to protect his lover as he rather be the strongest of the strongest. The sight of her cold body in his arms made him go insane. First his brother now the love of his life. But what happens when she reincarnates into the Taisho period as a Hashira? It's her duty to kill all demons after all...