Classmate of Takashi Komuro. They have known each other since kindergarten. When they were young, Rei promised to marry him when they were older. She has loved him ever since but because of Takashi's indecisiveness, he was never able to honestly return her feelings. Heartbroken, she sought comfort in their friend, Hisashi, and ignoring Takashi at the same time in hopes of forgetting the pain. Rei was furious when Takashi killed Hisashi, even though he turned into a zombie. However, when Takashi was about to leave her behind, she quickly apologized and they amended their relationship.

Rei doesn't find it above herself to reprimand Takashi for acting carelessly. She worries about his well-being whenever he goes to fight "them". Rei has also proven to be a skilled combatant through the use of sojutsu ("Spear Techniques") 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, Shido purposefully failed her so she would have to repeat a grade. Rei bears a lasting grudge against him and feels uneasy whenever he's around.

Although Rei dated Hisashi, her feelings for Takashi never disappeared. In chapter 12, Rei shamefully admits that she dated Hisashi because he was cute and cared for her but says it is different now. She finally understands Takashi's personality and confesses that it is his selfless nature that she fell in love with. Rei also professes that she would do anything to be with him. Like Saya, Rei gets irritated whenever Takashi spends alone time with Saeko, even if they are fighting "them". As her feelings intensifies, her flirting has also become more aggressive on several occasions. She uses a Spear made from a broken Broom and later a M1A Rifle with a Bayonet attached.