It could also be a matter of drastic shifts in the sun - Remi's talk about having to train new fairy maids makes it pretty clear that Sakuya's passed away a long time ago (enough that the lifespan of nigh-immortal fairies is an issue) such that the sun is starting to go red giant and has boiled away the oceans.
Granted, that raises questions of how a space station would be able to survive, but given the vast amounts of time we're probably talking about, if humanity has survived that long at all, then it's probably using shielding and everyone's become a part of the singularity.
It could also be a matter of drastic shifts in the sun - Remi's talk about having to train new fairy maids makes it pretty clear that Sakuya's passed away a long time ago (enough that the lifespan of nigh-immortal fairies is an issue) such that the sun is starting to go red giant and has boiled away the oceans.
Granted, that raises questions of how a space station would be able to survive, but given the vast amounts of time we're probably talking about, if humanity has survived that long at all, then it's probably using shielding and everyone's become a part of the singularity.
Wait, if it's been so long, how is Keine still around?