The Fate Breakers Space Marines
The origin of the Fate Breakers is a mystery and a well kept secret amongst their ranks. But they are hailed as humanity's comeback and heroes to scores of worlds who are now free of strife and anarchy due to their actions.
"Humanity is on the brink of extinction, surrounded by alien enemies as Chaos spreads within. This fate shall be broken, this is your task until your dying breath."
-Fate Breakers Rites of Initiation, Line 1
The entirety of the Chapter is rarely seperated, traveling through space in a massive fleet. The main problem they come across on many worlds is that disorder soon erupts after the planet is left to fend for itself. The Fate Breakers solve this by rehabilitating the world. They set up an Administratum presence and a new government through thier arbitration, since many Marines are skilled politicians as they are soldiers. But this is not the only purpose they serve, the Fate Breakers have turned the tide of many conflicts of all sizes even when all hope was lost.
The contact with fellow Imperial forces is purposely limited. They might be considered heretics for how they follow the Codex Astartes. The battle doctrine they use dictates that is is better to die than repeat a mistake. So they go against the Codex if it will keep them from doing so. This has led to the expulsion of Techmarines and integrating thier knowledge into the average battle brother. This might make them heretics, but nobody has called them on it.