He must be choosing to live and stay living in Korea. The yearly paperwork and having to go to the immigration office every year is annoying (sometimes the wait line is an hour or more. been there. done that). Choosing to naturalize (and not get citizenship through marriage) is sweet and sounds kind of patriotic. Like. He is doing it in a way more Koreans would accept.

Identity is such a personal thing that I don't think anyone has the right to judge or criticize someone about how the choose to identify or demonstrate their identity. Just because you wouldn't renounce your citizenship to a country you were born in doesn't mean that it isn't valid or meaningful for someone else to do so. Really I don't think he has to explain to anyone his reasons for wanting to renounce his Japanese citizenship and we don't have to understand it.