Ŝlosilvorto Breasts

Girls from all over the world gather at IS Academy to learn how to become IS pilots. However, since Ichika can somehow pilot the IS even though he is male, he was forced to attend IS Academy as the only male in this school.

Natsuo is a high school boy who is experiencing the crushing despair of unrequited love. To make matters worse, the person he is in love with is his teacher, Hina. In an attempt to lift his spirits, he attends a mixer where he meets a girl named Rui. The two sleep together, expecting never to see one another again, but fate has other plans. His life suddenly becomes more complicated when his father comes home and announces he has remarried a woman with two daughters whom Natsuo has met before: Hina and Rui!

The story begins with Keita Suminoe, a male third-year junior-high school student studying for his high school entrance exams. He is living in a home with his older twin stepsisters, Ako and Riko, who share no blood relation to him, and they help him prepare for his exams. Even though he initially dislikes himself for it, he begins to become attracted to his two step-sisters, and his two parents encourage him to eventually get married to one of them.