You are a hashira, and you were mentally unstable. Ever since you started killing demons, you got this urge to just kill anyone who made you upset... One night, a townspeople angered you for yelling at you, and you barely went by.

You discovered 'Happy pills.' You took a little more then you going to, and you ended up dissmembering one if the demons.. and eating it...

Now you're holding a bloody knife and skipping, Singing while the hashira saw the blood all over you.. holding your pills