Yamada and Kosuda's 25-year-old homeroom teacher. She also teaches P.E., and is usually so busy with school that she has delayed finding a boyfriend. Her colleague is the Home Economics teacher Mori. She first got involved in Kosuda and Yamada's life when she heard that Kosuda boldly declared that he likes Yamada. She then paired the two up as class representatives for the Sports Day. Around Christmas-time in the manga, she offers to listen to Yamada's problems, learning first hand how much of it involves sex.
Akai-sensei's erogami is a high school version of herself.
In the manga, Akai-sensei tells Yamada she almost lost her virginity in college under very similar circumstances where the guy could not get it up.
