Krakia?

The moon appearing so close and seemingly within the ''grid'' makes me think it's not a real moon but the entire area is within a dome with an artificial atmosphere of some sort, maybe to simulate their own planet. It can't be in space itself in my opinion since you also see clouds in the sky, so it's not like ''stars, moon, blackness, it's space'', also since I believe someone said we're being invaded or something? That would mean we can't be in space since that would mean -we're- invading -them-, not the other way around.

They could have set up an area on earth, like a base and/or city where they can live like they normally would without being detected while they secretly get ready for an attack on the rest of the planet.

That's what I think though. Someone will probably point out flaws in it all though since admittedly I never once paid attention to the story surrounding Masteria whatsoever so I might be saying something that sounds totally ridiculous.