Oikawa is a very ordinary student, except for being a little sulky. One day during gym class, while he is captivated by Kawai-san, a carefree girl who he secretly has a crush on, a flying ball hits him in the head and he passes out. When he wakes up in the nurse's office, it's Kawai-san! Oikawa tries to stand up immediately, but he loses his balance and dives into Kawai-san's chest! What's more, Kawai-san notices Oikawa's certain part, which has been quietly getting bigger, leads to an unexpected development...!?