This manga consists of oneshots that are loosely connected with each other.
Chapters 1 & 3 focus on the new relationship between Shiba, a high-school student, and his teacher Onosaka. Things are not going well; sensei has an inferiority complex because Shiba likes large-breasted girls.
Chapters 2 & 4 are about Inuo (a friend of Shiba's, who's quite the player with girls) and Natsuda, a boy with whom he finds himself in a love hotel the morning after a wild party. Inuo would just like to forget everything because he's definitely not gay, but Natsuda wants to be his friend so badly that he can't turn him down. Natsuda turns out to be a cheerful and engaging companion, and Inuo starts to spend more and more time with him; going to movies and hanging out. But when he finds himself embracing Natsuda again, he pushes him away -- because he's definitely not gay!
Chapter 5 introduces Shiba's brother, Keisuke and his friend Aki. Aki wants to do more than kiss, but Keisuke only went along with the kissing because it was Aki who asked him. So now that summer break has arrived, he avoids Aki. But when Aki stops calling and avoids him in turn, he's not happy at all.
Chapter 6 is an unconnected oneshot called Yasashii Kuchibiru (Gentle Lips). Yuki and Kaneda are childhood friends, neighbours and more... but Yuki never seems to have time for Kaneda.
Chapter Extra: Secrets of a youth follows Kei and Aki three years later and now in high-school, dealing with some "growing pains".