Hellstar Remina/WMG

Planet Remina is also a Lotus Eater Machine

 * We saw a person becoming part of the planet after being exposed to its atmosphere. We also know that this was not just a case of the unfortunate astronaut just being melted by the atmosphere and fertilizing the living matter already present on the planet, because his eyes and tongue did not melt: instead, they were changed in shape and size to the same monstruous proportions of the tongues and eyes that were already present on the surface.
 * The ending wants us to believe that  How convenient.
 * What if, instead, planet Remina does not consume sapient creatures, but turns them into parts of itself, feeding their brains with false perceptions? This would explain the transmission of Kaneishi from the planet (his words weren't just misinterpreted: he was actually perceiving Remina as a paradise), while the ending would not depend from a Deus Ex Machina: the people who think of themselves as survivors are actually on Remina and suffered the same fate as that astronaut: their tissues became parts of the planet, while their brains are merely perceiving that they escaped.

Planet Remina is Human Remina after Time Travelling

 * Eventually, i.e. after one year, Remina and the rest of the survivors would die off, but Remina would first be driven insane by the ordeal (especially once supplies got scarce and she was tortured through starvation and etc., might even resort to cannabalism just to survive a little longer); the safe room would crash into asteroids and other space debris, creating a core for a planetoid. Remina's insane mind would remain, however, and combined with extraterrestrial life eventually formed the basis that would one day become the planet Remina. Because of the starvation she suffered through, as well as her desire to return to normal/life, Planet!Remina went about devouring worlds, gaining mass in the process. Then the wandering planet travelled through a wormhole and after finding its way (say, telepathic connection with her past human self), Planet!Remina returned to Earth and started the whole thing again.