This is a thing you can buy, today, as a model year 2019 car (I think based on leftover bodies from 2008 or earlier though).
...well, OK, kei car was a bit of a misnomer at launch, the 650 cc engine it had from 1988 to 1996 was 100 cc too large until 1990, and it was 2 cm too wide until 1998. (And, as it got a 750 cc engine in 1996, it was never actually legal in Japan as a kei car, except maybe in the low-volume electric model that Lada produced into 1998, but close enough!)
...and, OK, car is a bit of a misnomer too. It’s a FMVSS 500 Low Speed Vehicle, which is limited to 25 mph by law. And, this one’s electric (and I’d guess with lead acid batteries, although Lada’s own electric model had NiCd). But, if you don’t mind building it yourself, there’s a kit version sold without powertrain or batteries, that could be registered as a full car in many states.
...not gonna lie, I’m morbidly curious. Not enough to actually throw money at it, but morbidly curious nonetheless.