Hitomi Kashiwa

Satou's senpai in high school, now a public servant. Due to stress, Hitomi develops a dependence on drugs. Hitomi met Tatsuhiro when she persuaded him to join the Literature Club, though most of the time they only ever played card games. She has always been fascinated by the concept of conspiracy theories and introduced Satou to the idea.

Satou's longtime crush/love-interest, seemingly the only friend and the only woman in his past, or perhaps the only noteworthy or memorable one. Apparently had an immense influence on his life.
Acted as the catalyst for the actions that made Yamazaki idolize Satou in school and befriend him in the present, as Satou was just trying to show off and look cool in front of Hitomi-Senpai.
Took Satou's virginity in high school, giving him goodbye sex when she graduated ahead of him and left him alone.

It is revealed later that Hitomi is part of an online community at present, and plans to attend an offline meet on a private island where the group will commit suicide together.