Wakaranai Desu Yoshida-San summary:

Ninety-nine is a simple and unremarkable college student. As he is getting ready to go home after finishing his university lecture as usual, a solitary beautiful woman, "Migyo Yoshida," who is rumored to be a "mermaid princess," passes by. While the boys are in an uproar, 99 is secretly summoned by Ms. Yoshida. When they are alone, Mr. Yoshida presses him. In fact, 99 and Mr. Yoshida have an intimate relationship... However, he is unable to grasp the romantic distance between them because Mr. Yoshida is too expressionless, and he is having a sweet but bittersweet college life, unable to go from "friend" to "lover".