The wavering seed.

High school student Natsume Harumi has a crush on his biology teacher, Haruka Koba. In order to spend more time alone with Koba, Harumi purposely fails his biology tests so he can attend Koba's supplementary class. However, one day a student named Nei attends the class. On the first day, Nei sleeps through the whole class. He asks Harumi to teach him, and Harumi agrees.

"If you understand everything, then why do you need to take this supplementary class?"

Just one sentence from Nei, and Harumi can no longer hide his anxiety.

(Source: Home-sha, translated)