Comment by autumnstwilight

I am surprised by his situation as I know of the Zainichi Koreans here (Korean citizens who were born and raised in Japan and live here as an ethnic minority). My understanding of the situation is that they legally are able to naturalize and a significant minority of them do so, but many don't as they would have to renounce Korean citizenship.

I do find it quite unusual that he would not be allowed to naturalize after living all his life here and being married to a Japanese citizen, so perhaps there are other exceptional circumstances. Or perhaps his statelessness isn't something he is actively trying to resolve, having found ways to work around it when he needs to travel and do other things.

The immigration system in Japan is quite open and straightforward on paper, but can be far more challenging in real life.

I know someone who tried to start the naturalization process but was instantly shot down for his Japanese skill (he speaks Japanese well). I know others who have lived in Japan for decades but cannot apply for permanent residency because they only receive short visas, making them ineligible.

Immigration officers have ultimate discretion and will not explain themselves to applicants. I assume this is by design so that particular 'standards' can be subtly applied without being reflected in statistics or receiving any criticism.