[dragonwriter]

Japan doesn't have birthright citizenship (unrestricted jus soli) in the first place, it is a jus sanguinis jurisdiction with a very limited fallback jus soli (extending nationality on the basis of birth in Japan, rather than Japanese parentage, only to those whose parents are both either stateless or unknown.)

[Muromec]

There is a spectrum between giving citizenship to everyone born in a country (US) and not giving it at all (e.g. Thailand) and every country is somewhere inbetween with some kind of a qualifier and a procedure. Sometimes it's enough that both parents are in the country legally or have a residence there, sometimes you have to wait it out until you are 18 without hiding from reach of the state.

Practically, there is no point for the state to deny you citizenship if you went to school there and can do some kind of a job and pay taxes, because they can't even deport you to a country of origin if you are stateless and born there.

Technically even the US has the jurisdiction qualifier, which the orange clown wants to abuse.