Megami no Kago wo Ukeshi Mama no Saga

Cain, a young mage serving the Demon Lord's Legion, faces his mother, Luludiana, who wants him to leave the Legion. She and Cain's close friend, Priest Izneel, perform a secret ritual to strengthen their magic and confront him. However, each time they clash, Cain is forced to hear explicit details of the illicit acts between his mother and his friend!