Ero Mangaka to Ashi-kun

Kenji Kaga, an erotic cartoonist consumed by his unhealthy lifestyle, ends up hospitalized after falling unconscious trying to reach his deadline. His editor, not surprised by the number of times the cartoonist has reached that point, decides to hire an assistant to take care of Kenji. The appointed assistant, Rui Fumitsuki, turns out to be Kenji's biggest fan. The misanthropic Kenji tries to come up with a way to make Rui quit of his own volition. The plan? Masturbating in front of Rui with the excuse that it's part of his artistic process.

(Source: Ichijinsha, translated)