Heat death. The universe will eventually succumb to heat death in the distant future. The timescale is so vast that its end is beyond sight...
In the universe's late stage, most stars are red dwarfs, cradles of life. But the distances between star systems are immense, and resources within them are scarce. For civilizations relying on sublight travel, the journey is exceedingly long and dangerous. The extraordinarily advanced technology required for faster-than-light travel has weeded out civilization after civilization. The protagonist's predecessor civilization created them using biology developed to its utmost limits, then perished. Now the protagonist must search for a way to survive in this dangerous yet tranquil universe.
