Akuma no Kodoku to Suigintou no Shoujo

Sugarlia is the granddaughter of a fallen necromancer, who arrives on a cursed island. There, she meets Yoksal, a great sinner. Bearing countless sins and hosting a demon that turns solitude into power, his encounter with her changes the course of fate. A final love unfolds between a man who does not know love and a girl who knows only love, risking their lives for it.

(Source: Kadokawa, translated)