In'yoku no Jutsu ni Ochita Kon'yaku-sha o Me no Mae de Haramase Ryo Sareta / 淫欲の術に堕ちた婚約者を目の前で孕ませ陵○された勇者の物語

The story begins when you (the hero) form a party with a warrior, a wizard, and a priest and confront the "Dark Demon King" who has awakened from the depths of hell.
The heroic party manages to defeat the Demon King, but on their way back to the capital, your childhood friend and "fiancée," a monk, suddenly complains of a change in her health.
At the inn where you stayed, he started to masturbate at night, and he also pressured you to have sex with him...
According to a wizard who knows him, the "lewd prints" that suddenly appeared on the monk's lower abdomen suggest that he was probably exposed to the "art of lust" during his battle with the demon king.
Those who have been affected by the art of lewdness gradually become sexually lewd, eventually leading to physical and mental collapse.
As a result of the discussion, the party was divided into two groups: the heroes who were to return to the capital to report the defeat of the Demon King, and the wizards, warriors, and monks who were to go to the "village of wizards" to solve the problem.

After reporting the defeat of the Demon King to the King, the heroes entered the village of wizards a few days late, but what you see there is...!
After numerous "raging mausoleum scenes," will you be able to rescue your fiancée?