Reiko Mikami

and class 3-3 deputy homeroom teacher. She gives her nephew advice on how to make it through Yomiyama through a series of "rules". One of them is to separate the private life from school life, thus Kouichi addresses her as Reiko at home, and Ms. Mikami at school.

She is also revealed to be the extra/dead one. Reiko was murdered about a year and a half before the accidents started to happen.