Ok I need help to found an anime I saw a few years ago and have been tring look for it.But can't found it so I need help. Ok here is the basic about I think.

It is about this guy who is not human he looks like a human but can change to a robat or something like a robat.And the guy has a guliter in his back and plays just one song that sounds sad very sad .He learns to play it and what it is after he meets a guy from the steerts that plays a guliter for money.And he ask him what he is playing.Oh and there is this girl teenager or older that is looking for him after her fathers lab is destory by a monster.She has a little brother or sister. Plz can someone help me... There are more then 2 seasons.I know that for sure.Because in the seond he is looking for his brothers made by the father of the girl. His body is half blue and half red.Not 100% but I know that half is one color and the other side is diffenert color.