As far as I know, there isn't a limit of power / speed for kei car category. In the old days Suzuki made a kei car that was "too powerful", the government "communicated" with them, and they settled with 64hps. Since then all the manufactures self-imposed the 64hps limit, but it's still legal for someone to power up their own car.
Smart K is another non-Japanese kei car that's more powerful.
Smart K is another non-Japanese kei car that's more powerful.