Mesugaki-sensei

Mesugaki-sensei draws erotic manga for girls. When she offers to be a reference if he draws a manga for her, the protagonist accepts, but she has never seen a live dick before! He goes all out with the sex to make her understand her dismay at the sight of a live dick!

(Source: Mujin Comics, translated)

Note: Published in Comic Tsuyahime Vol. 004