Neighbors Hiro and Koji share a playful yet tense relationship until Koji proposes a "more efficient" alternative to their solitary habits: having sex. As they give in to their desires, Hiro discovers her own masochistic tendencies during a series of risky encounters in their homes. Their sudden intimacy quickly evolves, leading to a bold proposal that changes the nature of their friendship.
Kouji continues to assert his dominance over Hiro, pushing her into risky sexual encounters. The situation escalates when their friend Rin, the school's idol, becomes involved. Kouji manipulates the situation, forcing Hiro to watch as he seduces Rin and convinces her to betray her boyfriend, further cementing Hiro's role as his obedient servant.