Heat Death Crisis
The Heat Death Crisis was an event in the history of the Empire of Arckas. After achieving near limitless ways to create megastructures, scientists discovered that the rate at which the universe approached thermodynamic equilibrium had increased to the point where in the imminent future, the Empire of Arckas would effectively cause the end of all life. This was occurring as the Empire of Arckas had prioritized artistic merit over efficiency and energy conservation.
To resolve this issue, the femtobots known as the Anathema were created that would forcibly remove any megastructure that proved to be causing the heat death to accelerate. However, this resulted in civil wars as well as the Anathema being sabotaged in order to destroy entire galaxies.
The permanent solution ended up being a mass exodus of the Empire of Arckas into the greater multiverse, abandoning nearly everything they ever created. The only entities that were found to be left behind were Na'zrah and the Anathema. However, before the Empire of Arckas left, they seeded various worlds with life to ensure that a future galactic community may arise hundreds of millions of years later.
Even after these events, one group of Arckasians known as the Mavetians regularly returned to the universe to monitor it.