Politics behind Japanese nationality law.

There still is a lot of negative thinking towards foreigners in Japan mostly because of the Japanese "pure race" thing and the reality that Japan is a homogeneous country.  The homogeneous society culture and mindset has how they have lived in for centuries and don't see the significance to change. Where emotions of anxiousness and uncertainty factor is here. Many Japanese citizens might never even meet a foreigner in their lifetime. Then there’s the stereotypes of foreigners. Remember, their society prefers conformity. Conformity is an important expectant way of life in Japan.

That's where Japanese nationality law comes into place. The government of Japan chooses not to accept that many foreigners into the country island as the citizens think foreigners will just disturb that peace of life and won't be well accepted into the community. Also there is the legal process of immigration and neutralization.