University student Ren continues living alone in Tokyo, with her older girlfriend Yuri, an associate professor at her university. When summer break arrives, Ren brings Yuri home to visit her family. Her older sister, Yuu, comes to pick them up, warmly welcoming them both, and Ren finds herself deeply moved by her sister's affection. Yet in Ren's heart, there's another person she can't stop thinking about—her sister's childhood friend, Yuriha. As Ren repeatedly asks about wanting to see Yuriha, Yuri begins to feel a growing sense of jealousy. That night, Yuri makes passionate, intense love to Ren, who writhes silently, constantly aware of her sister in the next room. The next morning, Yuriha finally arrives. The moment Ren and Yuriha see each other, Yuri stands frozen in place, watching the two women face one another. Amid swirling jealousy and desire, the four women become entangled in a deeply passionate, emotional encounter.