Multiverse Muncher

There is a demon so powerful it scares even the ruler of the hells, it is known as the demon of consumption. It consumes everything in its path. This is no ordinary Demon; it is really a primordial being of Consumption, travelling to different universes to consume everything. But when it came to this universe, there was a group of heroes (one of each class) that led armies of their peers against this demon, and they won successfully, locking it away and preventing it from consuming their universe. This war caused the kingdom to fall, making way for the High Elves to take claim the throne because they live longer there and are wiser. 

The world has rebuilt itself over the next 7,000 years, the MM being nothing but a barely remembered legend, until Ukuni found the tomb, not knowing it held the consciousness and opened it, waking it up and dooming the universe to consumption.