The Crimson Spell, Volume 1 - Ayano Yamane

A young prince saves his little brother and people by taking up a curse sword. This sword will change anyone with the blood line from the royal family into a demon.

Prince Vlad sets off to find a wizard to see if he can set him free from the curse before its to late. He wear handcuffs while he sleeps to keep the demon he is become locked up. But if the handcuffs comes off while he's asleep he changes and the demon side if free. But he never remembers anything he dose while in that form.

The wizard Havi , finds out what it's like to see the demon side of Vlad one night when he takes the cuffs off him. but he brings out the passion in the demon that night. When morning comes Vlad doesn't remember doing anything but sleeping.

They head off to fight a dragon so Havi will get something in return of helping Vlad. But instead he kills it and has to save Havi life from entering the place that the dragon was guarding. The spirit of a young wizard was the dragon an he helps as well.

They start to go to a Wizard towns were Havi came from to see if they can look at some of the older books to learn more about the curse on the sword.

Havi finds out his old teacher was helping Vlad's father when the curse was but on the sword and that an enemy was the reason why there was a curse on the sword in the first place. Havi has to get Vlad out of there before he is killed by the other wizards for what he is.