Once upon a time in the Rareverse.
In the beginning, there was only a primordial slime in space.
Tiny as a dot in the endless vacuum, the newborn slime bathed in the bright lights of nearby celestial bodies. And it started growing.
Time passed. Who could ever say how long it was? Centuries, millennia, eons, maybe. The slime became big enough to absorb small gas clouds, wandering asteroids, dwarf planets, and even drifting spaceships from unknown civilizations.
The slime kept growing, adopting beautiful shapes and colors. Not-so-small-anymore, everything inside the slime started decomposing and recomposing. Eventually, all that movement and contained energy reached a critical mass point, and the slime burst open!