All the magicians refer to this world as "hell." To them and thousands of their worlds, which reside outside of this world, magic is natural phenomenon, but in the world of humans magic is erased. To magicians humans are the source of hatred, they despise humans, they see them as "demons" and would do anything possible they can to annihilate them.

In the worlds of magic, magicians who commit heavy crimes are exiled to "hell" as their punishment. They would be sent back to their home world only if they can accomplish one mission, to kill 100 wizards who oppose the magic government. However, there was no man yet who has succeeded in undertaking this mission to the end.

Agi Meizel is a criminal who was exiled to world of humans. She is still a young girl and for a young girl to go through this ordeal would be extremely difficult...

(Source: Wikipedia, LNDB, edited)