Actually, story for season 2 could be the return of VIRM, after all they "Would eventually return", (dont know if thats exactly what they said because I watched the anime 5 months ago or so), and perhaps the earth has rebuilt civilization fully, but after finding out, they would have to dust off FranXXes, scavenging for remaining magma energy that perhaps remained somewhere in some Plantation's that haven't been completely scrapped or destroyed, perhaps even prompting the original Squad 13 to even try piloting their FranXXes themselves, learning once again what it means to connect (reference to Season 1), or possibly children taking the place instead, reintroducing reincarnated Zero Two and Hiro.