Inma-kun wa Oshigoto Dekinai

The incubus Alkeros's graduation exam assignment is to have sex with a highly superior human being, Koutarou. However, Koutarou has erectile disfunction due to the stress of his corporate slave lifestyle! Al moves in with Koutarou uninvited so he doesn't miss his chance for sex, but it doesn't go so smoothly... "Today was supposed to be the day I make my move and give him an erection, so how did I end up being the one who's being touched and getting turned on...?!"

(Source: Frontier Works, translated)