18+ Doku no Ou: Saikyou no Chikara ni Kakusei shita Ore wa Biki-tachi wo Shitagae, Hatsujou Harem no Aruji to Naru

Thirteen years ago, a terrible monster called the Poison Queen attacked the Jade Kingdom. A brave party of adventurers defeated her, but in the process one of them was stricken with a curse. In order to survive, she had to pass it down to her own son. Scorned as a cursed child since birth, Caim Halsberg is hated by everyone except his late mother and Tea, a maid working for his family. While his father and twin sister reside in their mansion, Caim is forced to live alone in a forest hut. But everything changes when a certain doctor helps him to overcome the curse and claim its power. Having now become the Poison King, Caim goes on a journey to achieve his one wish—but he never imagined that his poison would have quite the peculiar effect on the beauties he meets!

(Source: J-Novel Club)