Due to their parents' remarriage, Nonoka and Yume become sisters. The two begin living together as siblings even before their parents do. Nonoka honestly reveals her sexual orientation to Yume and gradually starts drawing her in. For Yume, who has had almost no romantic experience and is already in a relationship with a boyfriend, her bond with Nonoka becomes a completely new experience. She is enveloped in deep emotions and pleasures unlike anything she has ever felt before, becoming so deeply attached to Nonoka that she feels unable to live without her.