the series was pretty "logical" at the start but now its just getting more ridiculous. like how the terra formars can apparently walk around with these simple clothes, or how in an developed society like japan they now have 120 underground people. Japan has currently 2.5k homeless people... in the entire country... now tokyo alone is supposed to have ~50 times that amount... even if we say that the 100 mio people living on the surface mean the populace of tokyo and not of japan that would mean that the homeless rate still increased by 50 fold compared to the population. Since 100 mio people in tokyo compared to 120 mio living now in all of japan somewhat matches.
Anyway not even america can ruin a society that hard lol. I mean current day USA got homeless rate of 2.3/1000 compared to 1.2/1000 people which is what this manga seems to have... so maybe it is possible although highly inprobable.
Edit: So we got some information from next chapter, there live 17 mio people in Tokyo rn, so 120k per 17 mio that is just an insane rate. 0.7% to be exact compared to todays 0.002%. Its even two times higher than todays homelessness rate in the USA, and sorry but from all we've seen so far japan does not seem like it fell down a dystopian nightmare.