"In the future, time travel is outlaw, used only secretly by the largest criminal organization.
When they need someone gone and want to erase any trace that the target ever existing, they use specialized assassins, like me, called the 'Loopers'.

And the only rule is, never let your target escape, even your target...

is you."

(When you get to notice that kanmusus and Abyssals have a very important similarity, that's the time when you find out the true identity of the Loopers)