To solve the country's low birthrate problem, the Japanese government set up Otona Kōkō (Adult High School). Adults over 30 with no sexual experience are forcibly enrolled into Otona Kōkō by the government. Eito Arakawa is a 30-year-old single man. He graduated from a prestigious university and works at a bank. He has received recognition for his work there. He is also physically attractive, but he has never had sex. One day, he receives an entrance guide to Otona Kōkō.