Ginga Kanashima (金島銀河 Kanashima Ginga) is a weapons dealer and the primary antagonist of the series.
His right hand had to be amputated and replaced with a prosthetic after it was shot by Sōji Kuzuhara back on the mainland. As a result Ginga is obsessed with and utterly despises Sōji, and he wishes only for Sōji to suffer.
It is not known what Ginga actually looks like, since he constantly undergoes plastic surgery to change his appearance. He was introduced in the story as "Daichi Tsuchimi" - claiming to be a pawn of Ginga (aka himself), with a face that isn't actually his own. During the course of the story, he undergoes plastic surgery so that he looks exactly like Sherlock Liverpool.
(Sections: Appearance | Personality | Chronology etc. forthcoming)