Sodom is Luka's powerful dragon familiar.
Sodom is presumably named after one of the two hedonistic biblical cities, the other being Gomorrah.
Sodom can be somewhat of a coward, and is terrified of crows as they often attack him for trying to steal their shiny stuff. He's also afraid of Hotsuma, one of the Zweilt guardians.
However, Sodom has also shown himself to be quite brave when protecting people he cares about. He's willing to attack opponents much stronger than himself in order to protect Yuki and his master, Luka Crosszeria.
Sodom also seems to have a big appitite, wondering if a hot spring is food and whether he can eat it.