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...