A 22-year-old brother visits his 24-year-old sister who lives alone in Tokyo and decides to stay over at her place. Ever since they lived together at home, the brother has had deep feelings for his sister, and he still can't hide them. Sharing a small one-room apartment, they end up sleeping together, and their intimate moments grow longer. Unable to restrain himself, the brother finally confesses his desire to touch his sister's breasts. At first, she firmly refuses, but touched by his sincere emotions, she gradually opens up to him. She allows him to freely touch her body—but only for a limited time of ten minutes. They enjoy various acts including kissing, breast play, and touching her genitals. As the brother continues performing cunnilingus, the sister begins to act differently. Overcome with desire, the brother can't hold back any longer and boldly penetrates her.