In the near future the world is conquered by monsters send by Satan. The human race tried fighting it, but failed and became their slaves. That untill something unnatural began happening with the youth.
Several of them had some kind of power stores in their body: fire, water, nature, ... All that you can think of, but they couldn't use it themselves. They needed a partner.
When someone with the power made a deal with someone without it, a tattoo appeared somewhere on their body. The one that had no power in the past, was able to use power, magic, that was powerfull enough to fight with the monsters.
At the same time the other collapsed until their partner stopper the fight.
The war has begun.
A school to search for a partner and practice fighting opened.