This page is where authors of I'm not you can collaboratively plan the plot of the story.
Long ago, on a planet far from Earth, a human-like biological organism evolved and developed advanced technologies for 1) the creation of artificial life forms and 2) space travel. However, there is no easy way to travel between the stars, so the human-like biological organisms never traveled away from their home star. Instead, they crafted an artificial life form that was well-suited for interstellar travel. Those artificial life forms, rather than being composed of microscopic biological cells, were flexible colonies of nanoscopic components.
Traveling much slower than the speed of light, those artificial life forms reached Earth and established a small colony, although most of their settlements in the Solar System are not on Earth. The aliens watched the development of life on Earth and made some genetic alterations to primate genomes since primates were most similar in form to the aliens. Those genetic alterations make it easier for the artificial life forms to integrate their components into human brains.
Most of the alien artificial life forms have no interest in revealing their existence to humans. Some of the aliens occasionally spend time on Earth, placing some of their nanoscopic components in the brains of humans and influencing the behavior of select humans.
The alien who is "inside" Sara's brain objects to the practice of keeping the alien presence secret from humans.