After being dumped by his girlfriend, Yuya is heartbroken and turns to his dependable, kind, and big-sisterly aunt, Hitomi, for comfort. Having always treated Yuya like a younger brother, Hitomi worries deeply about his sadness and tries her best to cheer him up. However, she unintentionally blurts out a blunt remark: "Maybe you're just bad at sex?" That single comment becomes the catalyst that drastically changes their relationship.