There are four realms: The mortal world, the demon world, the underworld, and the angel world.
Many centuries ago, pieces of a great relic of enormous power appeared on the mortal world. A cross-realm war began for control of the relic. Legends say that a group of mortal champions defeated the armies of all four realms and gained control of the relic, then disappeared.
Then, one day, a piece of the relic reappears.
Now, war between the realms has begun again and a new team of heroes must come forth and save the realms from their own greed.