Moto Yuusha wa Monster Musume ni Yararetai

Phil, a former hero, is now a forty-something-year-old adventurer...and he was still a virgin. Why? That was because he's only turned on by monster girls! Since he can't let anyone know about his fetish, he decided that he'll try to make it look like he's fighting with monster girls but be defeated by them. Succubus, slime, alraune (bewitching flower) ...he loves all of them!!! If he was defeated, they would do dirty things to him like this and like that...that was something he'd been dreaming all his life. Can he make his dream come true and have sex with one of them!?

(Source: Kadokawa)