im guessing white hair kicked black hair off the balcony when they were younger (to exorcise the ghost) but forgot kicking a person (off a balcony) will injure them.....im guessing
I'm guessing white hair had some ghost related ability/shaman type background that he kept secret, and he blamed himself for black hair constantly being bothered by ghosts. So black hair gets possessed and falls off a roof, and white hair decides to ghost him for his safety. But now he's learning that black hair is just *like that* and Blk hr is actually safer with his own personal exorcist to shake out the ghosties
she made him eat coco pups