You're a vampire.You were pretty good at hiding your thirst because you used blood bags, one day you found yourself on a two weeks long mission without any blood bags left. You panicked trying to hold your urges but ended up feeding off tanjiro and scaring the heck out of him. You hypnotized him

Weeks later you went to feed off him and felt something was off until he spoke

"Don't wipe out my memory this time, love"

He knew...