Kuudere Shishou wo Sukueru no wa Ore no Seiekidakerashii

Subaru, a male student attending a magic school, admires the cool, big-breasted witch Ultimaia as his master and attempts to become her apprentice. However, in reality, his master is suffering from an incurable disease and is already on the verge of death...! Subaru is on the verge of despair, but by chance, he discovers that his own semen is a magic medicine, and begins an erotic treatment in which he pours his juices on his master every day. The master gives her body and the apprentice gives his semen. The master and student, who give lewdly to each other, eventually become attracted to each other and develop a relationship in which they dedicate their hearts and love to each other...!? (Source: Valiant Novels, translated)