 If you liked
Dragon Eye
|
 ...then you might like
Kurozakuro
|
In both series, main characters have taken/inplant something non-human into their body, which given them great power. But if it's not controlled, they will go berserk. And they're both (slowly) turning into monster because of the power. They fight monsters, Dracules in Dragon Eye and Ogre in Kurozakuro.