When Suzune and her cousin Yuushin were younger, they didn't get along. However, now that Suzune is in high school, Yuushin reappears in her life after many years apart, and he's transformed into someone cool and attractive. Yuushin claims that their grandmother instructed him to "protect Suzune," and as a result, he wants to live with her. Although they're no longer children, Suzune is struggling to find reasons to resist the new Yuushin.