Joou-sama no Eshi

Fujimaki barely scrapes by in school grade-wise. But he thinks all is well, because he just has to quit school and become a top-selling mangaka. It is that easy! One day he catches his hyper-intelligent classmate Yukimori masturbating to eromanga in an abandoned room in school. One thing leads to another and he gets blackmailed into drawing eromanga for her.

(Source: MU)