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 ero-manga in an abandoned room in school. One thing leads to another and he gets blackmailed into drawing ero-manga for her.