Based on the erotic game by Ammolite.

Koike Saki is a schoolgirl, while Hamaoka Takeshi is a teacher, as well as coach of her at the school swim club. Their relationship at school is only limited to teachers and students. However, after finishing school activities, their relationship is a pair of lovers who live on the same roof. After Takeshi's fetish was caught being that he likes BDSM, Saki was disappointed with his boyfriend's behavior, and also with his tsundere nature. Then what will they do next? Will they have sex with BDSM style?

(Source: Translated and Edited from Nekopoi)