There was a manga I read about 3 or 4 years ago and I'm having some trouble trying to find it again. It was a shounen manga, and the premise was that a girl was trying to either capture the most monsters, or become one of the best monster hunter in the world. She encounters someone on her travels who says that he's a monster trapped in human form, and he had bracelets and a neckband that enabled this. If I remember correctly, he was a sort of monkey-dragon hybrid, and that at the beginning he was able to morph one of his arms into one much larger that was covered in scales and had claws at the ends.
The girl at the beginning was able to control his transformations, and the monsters characters goal was to regain his true form.
I can't remember much else besides that the boy had orange hair and was rude, that there was another character introduced that led to a dynamic similar to the main cast in Naruto, and that they had all three joined a monster hunting guild.
Any help appreciated!