Arima

Arima (有馬; forename unknown) is a character mentioned in Shiny Days. She was a middle school teacher at Haramichuu, where Makoto and several other characters attended.

Otome mentions her to Setsuna as they and Ikeda are helping with preparations for Haramihama Shrine's summer festival. According to Otome, everyone in hers and Makoto's class fought a lot, so Arima-sensei, their homeroom teacher, did her best to make everyone get along. Makoto and Ii looked up to her, so they reportedly changed their behavior, as did Otome.

However, when Makoto and Ii started a "no romance" rule, things got weird when Ai and Reisei both fell for Makoto.

Later, without Arima's presence, Ii and Ikeda reportedly fell out with Makoto, presumably due to his popularity with girls. Because of this, Otome claims to have made a point of talking to Makoto whenever she saw him alone at the beach.

Trivia

 * Ai can also mention that Makoto liked to stare at Ms. Arima's bosom during their middle school years.