One idea I had a while back, but never took off, was the idea of the Yu-Gi-Oh Apocalypse. Essentially, due to some fuckery involving shadow magic, one of the big cities is now over-run with rampaging Duel Monsters. Good news, though, turns out that the monsters in your deck are now real as well. So, it's sort of like Pokemon... Only where you can't capture the pokemon, and instead of just trying to go about their merry business, their merry business is trying to eat your soul.