Legion I have some advice about your character. This i my personal opinon so feel free to ignore it. But I have a question concerning David's weaknesses.

You said - The very power he uses can and will kill him if he isn’t cautious. To make things worse he doesn’t even know exactly with what he’s dealing. Finally, it’s not excluded that Wizards might hunt him down, kill him and steal the crystal in his stomach. But he would have no idea why he’s being attacked.

The first weakness, is kind of pointless, unless you really intend for him to die for his own powers. I like the second weakness, I mean, if you actually roleplay him messing up a few times. The third is a little weird, do you really intend for him to be hunted? That's not really a weakness, it's a DANGER. I think ou should make an actually physical or psychological weakness. Like he can't use his powers properly if he isn't in the light of the sun or moon or something like that. Or something even as simple as he's afraid of fire, etc.