In this world, there exists a "second s**" classified as "Dom" and "Sub." A "Dom" has the desire to dominate a "Sub," and a "Sub" has the desire to be dominated by a "Dom."Most people are diagnosed in their early teens, but Chigusa awakens as a "Sub" only after entering university. When she feels unwell, her neighbor and senior, Rushi, comes to her aid. However, in the presence of Rushi, who is a "Dom," she cannot control her first heat...!?A fated love between two people who cannot resist their instincts!