The Satsujin Double Six is an assassination organisation situated on the SD-S Island Base.
At some point, Hardware Quadroceptus, head of the Galahad Arms, came into contact with Jecht Satsujin. Jecht was paid a large fortune to operate as a supplier to the Galahad Arms.
Further Reading: Satsujin Family
The Double Six's leadership contains only direct members of the Satsujin family, of which the organisation is named. Not all of the blood members are acceptable for leadership role, however, as Jecht is not one of their leaders.