GetBackers/WMG

... spoilers for the manga ending below, in spades.

When Ban was sent to live with Maria,

 * We know it's possible to go between them, and plenty of characters have. Ban's grandma seems to have very little presence for someone with such an interest. It would be reasonable for her to have a spy, or at least to have wanted to have a spy. And he was said to be 'dead' ...

Ginji is, in reality, the God of the Unlimited Fortress
It might explain almost the whole story. Even how they managed to escape situations that were almost impossible. Also, don't enrage a God, or he might smite you. With thunders and lightnings.
 * Well, this is true to a certain extent.