Natsuki, the beautiful queen of the university photography club, has a reputation for having relieved countless men of their virginity. Hirata, a younger male student, belongs to the same club but has eyes only for Natsuki's older sister, Fuyuki. Fuyuki is a thirtysomething virgin, an iron-willed woman who has built a fortress around her heart and remains firmly inexperienced. Despite the stark contrast between the two sisters, Hirata persistently pursues Fuyuki, slowly chipping away at her resistance. As Hirata and Fuyuki gradually grow closer and eventually manage to go on a trip together, it emerges that Fuyuki carries a deep emotional wound from her past that has kept her closed off. Meanwhile, Natsuki, who initially supported Hirata's efforts to win over her sister, begins to develop genuine romantic feelings for him herself, creating a tangled love triangle. The story follows the push and pull between the guarded older sister, the persistently earnest younger man, and the sexually liberated younger sister, leading to a conclusion where Hirata must choose between the two women and Fuyuki must confront her past to decide if she can finally open herself to love.