There was a legend from the time of deities and demons. The legend known as Everblade. A weapon so strong that it's wielders could barely hold onto it for more than a few seconds before being completely taken over by the soul of the weapon. As time passed on and deities and demons returned to their own demensional plane, the Everblade was not forgotten but became a myth, a folk tale, a story to pass down to kids before they went to sleep.
As meteors fell onto modern day earth like rainfall, the Everblade crossed over worlds and landed in the hands of a Japanese man. Changing its shape, it became a katana slicing through all of the meteors in the sky.
The meteors on Earth cracked open and it spewed out seeds in the number of millions per meteor. In each seed, based on its colors, out came monsters, herbs, dungeons, items, and the only hope for humanity, classes.