Season 1 of Oppai Heart: Kanojo wa Kedamono Hatsujouki!? premiered on October 28, 2011.

Ryuya was given the special task of sleeping with his girlfriends from school to alleviate the symptoms of a strange virus. One day, they drank a mysterious juice, after which the girls became infected, and from then on, they become permanently aroused. Moreover, their breasts keep swelling, and the only way to cure them is to impregnate them. But among the girls affected is his sister, who is nevertheless more than willing to devote herself to his member and have his child…