As I think about it, I think it similar to when Macross SDF-1 returned back to Earth on the last episode. People build their houses outside and just left Macross like a museum. It’s something like that.
I'm simply offering some example and see if anyone interested in RP like this. feel free to reject the idea.
Taking another liberty, since it's not originally my idea then I think some 4 to 6m tall mecha. aliens.. ranging from dog (the big one), horse-size, equal to the mch 7m giant, to a 16m tall t-rex size. so it's a stomping fest before the big boys entered the arena. large talons, claws, teeths, acidic breath, yeah I want them to be nasty. No range attack for them tho since it's going to be unbalanced.The mecha should be small otherwise they'll easily stomp on the aliens--what size?
Do the aliens have large talons?
I still think the rpg about 3 fat guys from Jersey selling used mecha and eating sausage and peppers while discussing pizza etiquette is the best so far.
Actually if you're not joking, the 3 fat guys as Old City rare surviving inhabitant, living by running their junkyard facility deep inside could be good additions to the game. Imagined survivors face when they encountered them inside and forced to spend their money buying equipments from them.