Haruna_Tenshi
Demon Slayer x The Case Study of Vanitas crossover
What if the Winter Spirit King of Winter took in Vanitas and Mikhail after the death of the Vampire of the Blue Moon? What if Noé, Dominique, and Jeanne were kidnapped and experimented on by Moreau as well?
The storyline starts when Vanitas returns to the estate he shared with Y/n and Isfrid since their reunion. He comes home to see Y/n's bloodied corpse on top of Mikhail's dead body, with Y/n being turned into a demon.
That is where things went from terrible to horribly worse upon Y/n conquering the sun while battling a Hashira, who was her own brother, Isfrid, who became a Hashira in one month after being an official demon slayer at 15.
Now, just like the humble Tanjiro Kamado and his demon-turned little-sister Nezuko Kamado, Vanitas become a demon slayer in hopes of turning his beloved snow bride human again.