In this world, there exist those with a "second gender" known as "Dom" and "Sub." Doms have the desire to dominate their "Subs," while "Subs" desire to be dominated by their "Doms." This condition is often diagnosed in the early teens, but Chigusa's "Sub" side awakens when she becomes a university student. When she is feeling unwell, she is helped by her senior, Tomoji, who lives in the room next door, but when she sees Tomoji as a "Dom," she is unable to suppress her first-ever arousal...!? A fateful love story between two people who cannot resist their instincts!