Reapers refer to a long line of people who are charged with governing the laws of death.
Reapers have existed for as long as death itself has existed, their duties being to bring balance between life and death. Reapers are chosen completely at random from any person in the world, and only at the instant the previous Reaper has died.
Every Reaper since the first has wielded the Death Scythe Corvus, which has the ability to kill any living thing with one swift strike. All Reapers are also able to see death in others, giving them the ability to wield Corvus. The ability to see death allows a Reaper to see the fate of all living things, allowing the Reaper to strike with Corvus, bypassing any appropriate "cause" of death, allowing for the death of things that would otherwise be unkillable.
In other words, the power of a Reaper is not so much the ability to cause death, but the ability to erase life.
- The Reaper's powers are partially based on the Mystic Eyes of Death Perception, but they are only able to work on living things and erases life instead of "stopping" the existence of anything, living or non-living, in the world.