Sisters and younger brothers who reunited in the countryside in midsummer for the first time in several years. Nobu is very interested in erotic things and makes suggestions to Jiuqu. "I'll massage my sister's milk, so let's massage your sister's milk." They immediately put it into action. Then, from Yuki, "Everyone has had sex? Is it really comfortable?" With that one word, they had sex for the first time in the name of practice. And the four adolescents know the pleasures and will spend days having sex if there is a chance like a monkey.