Crimson Spell

Crimson Spell (クリムゾン・スぺル, Kurimuzon Superu) is a manga series written and illustrated by Ayano Yamane. It is licensed in North America by SuBLime and in Germany by Tokyopop Germany.

Plot
Prince Val is forced by circumstance to use his family's cursed sword, and so he seeks out the services of Halvir, a sorcerer to help him lift the curse. They travel to find the materials to help lift the curse. The curse is unknown to Val, but it manifests itself as turning Val into a bloodthirsty and lustful demon at night. Halvir subdues the demon by having sex with it, and when Val awakes, he remembers nothing. Over the course of the manga, Val and Halvir meet several new allies that accompany them in trying to defeat Val's curse.