There are four forms of evil in the world. The thieves, murderers, rapists, and torturers. They can be found individually or in any combination. Those that are all four, however, are barely human. The souls of these sub-humans are so evil that it takes a solid form. Depending on which crime they excel at, this manifestation of evil takes on one of five different shapes.
The evil of these shapes is so pure that it cannot end naturally, and so is reincarnated into another being, to be recycled endlessly. This is how it was for centuries until the discovery of the Board.
The board is an ancient artifact that can harness these souls. When one of the evil beings dies, their soul can be sent to the Board, where it slowly begins to fall. When the souls fall into a row, portions of them are eliminated perfectly.
After the discovery of the Board, a guild was formed, dedicated to slaying these evils and eliminating their souls. One member of the Guild is at all times at the Board, and these few who can master the artifact are known as Boardmasters. The other members are around the globe, finding and killing the people who harbor these souls so the evil they carry can be eliminated once and for all.
The Boardmasters, arguably the most powerful beings in the Guild, all started as slayers of mortal evil, and were eventually strong enough to end the immortal corruption of souls. They live by one motto:
I am the man who arranges the blocks
that continue to fall from up above.
They come down,
And I spin them around
'Til they fit in the ground
Like hand in glove.