(Ignore the pics, they're just there so this post isn't a wall of text)
In ancient times, many millenia before even the Sage's of Six Paths era, a highly evolved civilization of humans lived on earth. A group of them, led by Seimei (see my previous post), practiced a form of science that bordered on magic. With it, they were able to manipulate the DNA of organisms, convert energy into matter and vice-versa, and even generate exotic matter to create miniature wormholes for transporation.
Their greatest ambition, however, was "the synthetization of life", which they eventually succeeded in, creating both a species of vaguely plant-like homunculi that could "feed" on the bioenergy of organisms it came in contact with, as well as merging their own bodies with their technology, augmenting themselves until they completely stopped aging.
However, immediately after this breakthrough had been achieved, a technological singularity befell their country, with the artificially intelligent plant-homunculi going out of control as they started rapidly draining and killing off any life on the planet. Powerless to stop their own creation, Seimei and his people had to watch as their formerly thriving nation was completely eradicated and turned into an uninhabitable wasteland devoid of any life.
Everyone was killed except for six individuals who escaped the plant-beasts rampage by fleeing into the void of outer space: Seimei, Isshiki, Kaguya, Momoshiki, Kinshiki and Urashiki. From there, they beheld something peculiar, something their research had not predicted: The more life the homunculi consumed, the more they devolved back into lifeforms similar to gigantic versions of regular earth trees, and started bearing strange fruits. With nobody to harvest the fruits, all the energy they absorbed within their bodies continued being accumulated within the fruits until the beasts themselves started dying off one by one.
Over time, their lifeless bodies and overripe fruits were absorbed back by the earth, and slowly, new life began to sprout from the planet's dead soil. Seeing as earth's evolutionary stage had been set back by many thousands of years, the six last remaining proto-humans decided to start traveling the universe in search of a new home world. They took with them seedlings of the God-trees they had created and left on earth the genetic seeds of all the species that had been inhabiting the planet before this apocalypse, including their own former human genetic material. With the vague hope that one day, millions of years later, life on earth may have evolved back to a state where they could return, the six last and first humans, dubbing themselves Oh-Tsutsu-Ki ("Those of the Great Hollow Tree") turned their back on their home planet and ventured on their journey through space...
