this is Boukon. he was once an angel, but he was prisoned for a crime he didn't do. his real name is kibou, that means hope. he was given the name Boukon after he was prisoned, Boukon means departed soul. in prison they burned he's wings so he couldn't flee or escape. it was also a sign on that he was once an angel. the tattoo on his chest is "aku" and means evil.
but he did manage to escape a late night by pulling out his chains from the wall. he used the stones at the ends as a weapon and he carries those changes whit him to remind himself how he suffered back then and how they let him suffer. (he's not really evil, he is good after some time, but in the start he's a bad-ass xP)