Yomi
About
She actually was bullied at her school. She finds a girl who is bullied too and becomes friends with her. Yomi pretends she's bullying her friend and throws her off the roof of the school. That was actually because she was planning to cause an explosion and kill everyone in the room including herself and she wanted her friend to stay alive. In the explosion, Yomi's body was cut in half and the bottom half was never found.
Yomi's ghost still remains in the school and it's said that if you go to the school building exactly at 00:00 on the new year's night and bring her a gift she will grant you a wish.