Because of an accident a year ago, the main character Yuuki developed a mistrust of women. Fortunately, it was actually a misunderstanding that was cleared up by Sakuya, so that Yuuki could get together with his childhood friend Eri. But as a price for her help, Yuuki was forced to have sex with Sakuya.
Ever since then, while trying to be Eri's lover, he's also been forced to continue his relationship with Sakuya...