Legion I also known as the Harvesters.
They are the only other (than the breeders) Devil Legion that can travel freely on the Prime. They serve Death. They roam the spirit, ethereal and shadow plane and harvest souls to return to the Halls of the dead to be judged.
Even though everyone fears the reapers. They are quite harmless on the prime. They cannot harm a mortal and are oath bound to guard the halls of the dead.
Reapers act solitary when in the Prime and there is a strict hierarchy. Every reaper has another above them and one below. The highest ranking Reaper Arch Devil Thanatos answers only to Death and the lowest ranking reaper is the most recently ascendant.
Sometimes referred to as angels of Death the term is actually already used from a celestial force that has long since been defeated. The only remaining angels of death Served one of the first incarnations a silver dragon that was consumed by the fires of hell before even the blood war started.