I suppose the modern day introduction to monster girls in the mainstream would be Okayado and his Daily Life with Monster Girls/Monster Musume no juu Nichijou, but that's a manga/anime. Maybe the Monmusu DMM spinoff? Although I can't remember if that was ero or not...
Monster lord is fragile just search in rrl not sure if the name is right though the keyworsd are monster lord and fragile