Koi, a university student living alone in Tokyo, has an older girlfriend, Yuri, who is an assistant professor at the university. During summer vacation, Koi takes Yuri home to visit her hometown. Yuri, Koi's older sister, welcomes them with a look of joy. Koi has someone she really wants to meet - her sister's childhood friend, Yuria. Yuri is jealous of Koi, who keeps asking Yuri about Yuria, and that night, she desires Koi's body more vigorously than usual. Koi moans, suppressing her voice while worrying about her sister in the next room. The next morning, Yuria comes over. Koi meets Yuria, and Yuri looks on...Four women are entangled, driven by jealousy and desire.