外務省：.pdf

The Ministry of Justice in Japan explains that choosing a nationality is an important duty for individuals with dual nationality. If a person has a foreign nationality and Japanese nationality, they must choose one nationality before reaching 22 years of age. The choice of nationality can be made by renouncing the foreign nationality or by making a declaration to choose Japanese nationality. The methods of choice include submitting a notification of loss of foreign nationality or a declaration to choose Japanese nationality to the relevant authorities. Individuals who have acquired Japanese nationality through naturalization or notification of acquisition of nationality and still possess a foreign nationality must also make a choice. The Ministry advises consulting with the government or diplomatic mission of the foreign country for further details on the procedures for choosing a nationality.