For Simplicities sake the true names of the Reapers and what the Scythes are known as to the rest of the galaxy will be omitted from the fluff and replaced with the Terran terms “Reaper” and “Scythe”.
     The Reapers Scythe or, “Scythes” for short are a large, brutish species that were “uplifted” by the Reapers on one of the first planets they scavenged. The Scythes, or as they were known then the Jiktai,  had entered a perpetual state of war and had managed to rebuild their civilization up from apocalyptic conditions seven times over the course of their long and mostly forgotten history only to reset their progress with one mass-extinction level event after another. They showed no signs of slowing down when the Reapers found them.
     Their Scavenger outpost was initially met with great hostility and conflict but, eventually, they convinced a small, young, faction within the Scythes to ally with them. They were granted small technologies at first, to give them a taste of what the reapers had to offer and over time, managed to develop such ties to the Reapers that they were given cybernetic upgrades, from complete neural revamps to incredible cybernetically enhanced strength. With these tools they slaughtered all of the other Jiktai and officially swore to their new master, becoming their “Scythes”.
     That was long ago. Now the Scythes, seeing the Reapers as deities due to careful and deeply ingrained indoctrination, act as a vanguard and as muscle for the Reapers when they scavenge worlds and when they do business with other intergalactic civilizations. Outposts on new worlds generally don’t have the best of the best of the Scythes instead being mostly manned by the younger, fresher Scythe Minors. There is a single Scythe Chaplain who is an old veteran Scythe that acts as the Spiritual, Military and Cultural leader of the people. Guiding them on how to best serve their gods.