some thoughts about the wind breaker scifi au, in no particular order:
definitely a 'most of humanity lives in space' type of situation. luxurious space stations were constructed for escapees to live in. you either got in through connections or were lucky enough to win the ticket lottery.
those not lucky enough for the luxury model were evacuated to less... stellar construction. it did the job! it's just obvious that corners were cut for the luxury model. these were the humans who decided after some time that they missed earth and began the process of recovering patches of the planet.
bankoku-gai was among the first, on the very site of their old city. makochi came later. there are other cities scattered around the globe, hubs of human and alien activity alike. the tsunaba district is made up of descendants of those who were never lucky enough to flee the dying planet, but were able to survive.
keisei street & makochi have an alliance, since they're close to one another. shishitoren's turf is in a yet unrebuilt section of old makochi so it's mostly ruins except for a few scattered shops.
something something. it was aliens who came to humanity's rescue in their hour of need and gave them the technology to construct said space stations in the first place.
there's a lot of people on earth who just want to live peaceful lives but there's just as many who choose to live on earth because they want to get away from legal authorities. these two forces inevitably clash.
the last thing sakura remembers, he was on the train heading to his new town. the next thing he knows, he's found himself in a totally different place with strange creatures and mystifying technology. he doesn't remember how he got here or what exactly happened.
but also. he knows a punchable face when he sees one. and those jackasses bothering that girl have very punchable faces.
sakura's very unsubtle attempts to get information from kotoha while she's much more subtly trying to get information from him. never seen you in these parts before. you from around here?
pov: you are kotoha. you are slowly piecing together that the vaguely suspicious guy who rescued you is a time traveler. yeah. she definitely needs to call ume.
umemiya is like welp! i know what to do! you should enroll in furin and join my gang!
oh my god sakura's apartment literally is just a ruin.
kotoha: do you have a place to stay?
sakura, thinking about the abandoned apartment that he's been using as shelter: yeeeeesss....?
hello what if togame is a broken down android that choji digs out of the trash. he fixes him up and gets him running again with the help up of his friends (mostly with wanijima's help let's be real). this is great! you should join our gang!
(togame has no idea how to fix choji as he's breaking down. humans don't come with a manual.)
togame challenging sakura to a fight and hiragi's just. hold on. he's human. and sakura just snaps like HAH? WHO CARES? LET'S FIGHT, SCRAGGLES. and only finds out that togame is an android later.
(and yet, he still holds his own)
TWO HOUR COMMUTE CANCELED. TELEPORTERS REAL.
(you are NOT getting Sakura's ass in one of those.)
kiryu was born and raised on one of the luxury space stations but he got sick of it all and thus in an act of rebellion enrolled in one of the few existing schools on earth.
(he and akari may or may not be designer babies)
what if tsugeura is a four armed alien. now he can do DOUBLE THE FLEXING. he came to earth with his family when he was very young as refugees. makochi is open to anyone who is willing to live there and help out.