Classmate and childhood friend of Takashi, they've known each other since kindergarten. When they were little she promised that one day she would marry him. Despite liking Takashi, their relationship was at odds at the beginning of the manga due to his indecisiveness. It was then that she started dating one of his friends, Hisashi, since he wouldn't make a move. As the story progressed they ended up reconciling their relationship. She doesn't find it above herself to reprimand Takashi for acting carelessly. She worries about his well-being yet admits that his selflessness nature is one reason why she fell in love with him. Headstrong and reliable, Rei has proven to be a skilled combatant and strong asset to the group. Initially in the same year as Saeko, Rei was held back despite being an excellent student. Her father- a police detective- had been investigating the corruption behind the father of Shido, one of the teachers at her school. As a result of this he held her back purposefully. Rei bears a lasting grudge against him and feels uneven whenever he's around. After having escaped the high school and resting at the family mansion of Saya, she and the group are in search of their parents.