Demon Lord Mara's Lustful Academy ~The Hero, Corrupted into a Teacher~

Train the hero and transform them into a lustful monster!!!! The world has been invaded by mysterious entities called monsters, and humanity, to counter them, created superhuman soldiers called "Heroes" and engaged in fierce battles. As time passed, the setting shifted to the "Hero Academy," an institution for training heroes. The two sisters, Sakuya and Kaguya, female heroes, lived harmoniously while fighting monsters. However, they were captured by Demon Lord Mara and subjected to intense and lustful training!!! As a result of Mara's training, the two transformed into monsters, becoming Mara's obedient servants. What is Mara's true purpose in training the heroes...!!!? Is it to give the heroes a lustful education!!!? A training fantasy in another world!!!