Mitharos at 15 years of age was helping the angels AND demons fight the destroy the rising kaiju threat. But the threat was so great, that they had to use human weaponry and deploy a...nuclear bomb. They bombed the battleground while Mitharos was in it, and radiation was his greatest weakness. The other kaijus didn't survive, but Mitharos was nowhere to be seen.

A few days later, he washed up on a shore, bleeding a lot. The demons and angels now saw him as the last major kaiju to deal with, and so using their magic, shrunk him and imprisoned him in a crystal....but they never knew that in the future, they willl regret for what they did, just like that old saying..."One finds his fate more quickly when he tries to avoid it."