Posthumous divorce’s technical but less popular name is a “notification of marital relationship termination” (inzoku kankei shuryo todoke) which means one is officially severing ties with the family of a deceased spouse. What’s particularly strange about it is that it doesn’t really serve any purpose for a vast majority of people aside from a government-approved official statement that someone finds their in-laws unbearable.
The Japanese government wants people to choose citizenship by the end of their 20th year, because 20 is the age of majority in Japan. But if you don’t say anything, they won’t ask, and you can keep renewing your Japanese passport along with your other nationality’s.
Oh right, 20. Thanks for the reminder, I mix those up. I’ll edit my comment haha