The siblings gather alongside the other ARES members.
I'm gonna kill everyone in Toman myself.
It's also mentioned that under Izana and later Shion's ruling, Black Dragon went from a respectable gang to committing all sorts of heinous acts.
But there are about 15 gangs from multiple timelines that play heavily in the course of the manga, which are listed below from least to most morally corrupt.
Rhadamanthus later uses his power to command Kozuki to bring the Ark.
Was once the 9th leader of the Black Dragons, something he never gets tired of mentioning, and still has the attitude to match.