I find it interesting how much the idea of a name can be between different cultures. In the UK, your name is defined by use (although these days there are more databases and records). The courts acknowledge that a person can be known by two different names and names are defined by usage.

In Japan, generally speaking, you're not allowed to change your own name. You have to ask a judge for permission and have a valid reason. I personally, having not grown up in Japan, find it very odd that the state enforces what your name is, perhaps even under protest.

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.