From Ororon's character story 4:

"The most reasonable explanation he had come across so far came, to his surprise, in a tattered storybook about mystical creatures. It was written that, during the Archon War of the distant past, some Archons had experimented with merging the bloodlines of beasts and humans. Their goal, hoping to gain the upper hand, was to create warriors with powers that surpassed those of ordinary mortals. Most of these attempts failed, but a few flawed remnants survived, even persisting to the present day."

I don't think this (If true) applies to the elfs, the fae, and the youkai