Love & Piss ~Shoujo no Gaman ga Sekai o Sukuu~

In this world, your magic power increases by holding your pee. Yurika is a magician who severely lacks pee and decided to summon a guy who is able to store a lot of it so that he can supply her with it through a special ceremony (sexual intercourse) and allow her to pass the make-up wizard test. Yoshifumi was the chosen one and was forced to help her out since he couldn’t return to his own world until she becomes a wizard. Also, his childhood friend Yumari was also brought to this world at the same time, and for some reason she is also taking the wizard test with Yurika.