He's an ordinary college student living in Tokyo, who has never had a girlfriend before. One day, he visits his part-time job friend Y-kun's house and meets his younger sister, O*chan. She is the complete opposite of his plain, quiet type—a trendy, modern-day gyaru who's up to date with the latest fashion and culture. She keeps asking him questions like "Do you have a girlfriend?" and "Have you had any experience with girls?" Her curiosity and boldness become a constant source of excitement for him. This encounter with her becomes the turning point that drastically changes his life.