Not too much is known about the crime syndicate. It is an East Asian Triad and Yakuza-inspired organization led by a group of mysterious elderly men who are called The Van. The Van are usually seen wearing imperial Manchurian-Chinese clothing of the Qing Dynasty. The Syndicate specializes mostly in assassinations, but are also involved in the trafficking of narcotics, Red Eye in particular.
The rules of the Syndicate states that members who attempt to leave, or fail to complete tasks, are punished by death. Mao Yenrai served as a captain or Capo to the Elders and was a mentor to both Vicious and Spike. He is most likely the one who brought them into the Syndicate (since entering into a major criminal organization usually requires sponsorship from a higher-ranked member).
Spike and Julia used to be members of the Syndicate, and they planned to elope together. Spike was to fake his death and rendezvous with her. However, Vicious finds out and forces Julia to choose between killing Spike or to be killed herself. Instead, she chooses to run away; to protect Spike, she never meets him at the graveyard. Spike left and ended up becoming a bounty hunter, Julia lives a life on the run, and Vicious plots to overthrow the Van and take over the Syndicate himself, as well as to fulfill his promise to kill both Spike and Julia.