High school boy Harumi Natsume has a crush on his biology teacher Koba Haruka. In order to spend more time alone with Koba, Harumi purposely failed his biology tests so he could attend Koba's supplementary class. However, one day, a student named Nei attended the class. On the first day, Nei slept through the whole class, so he asked Harumi to teach him. Harumi agreed.

"If you understands everything, then why do you need to take the supplementary class?"

Just one sentence from Nei, Harumi can't no longer hide his anxiety.