Becoming Japanese

Actually, a passport is not proof of nationality. A Japanese family registry is, however. This question was actually posted in the Reddit group "Residents in Japan" , and I answered it there, but unfortunately the moderators removed the good question (in my opinion) due to their strict rule of requiring its participants to actually reside in Japan. Thus, I will re-post my answer here: The worst case "penalty" for not properly getting rid your original nationality or re-acquiring or re-instating your old one or getting new ones is that they can unilaterally annul ("cancel") your Japanese citizenship on the grounds that you did not properly complete all the mandatory required steps to obtain it as prescribed by the nationality law . This procedure is called "administrative denaturalization": the loss of citizenship by an annulment of naturalization without the government needing to sue them in a court, also known as "adminis...

The clock gets rolled back for the U.S. case Whether you relinquish/lose your nationality (which is a requirement for Japanese naturalization) before the naturalization process completes or afterwards depends on the country of your original nationality. Japan would probably prefer that you lose your nationality prior to receiving your Japanese nationality, as it is a prerequisite for receiving Japanese nationality and is easier to verify and enforce when done beforehand. Statistically speaking, the vast majority of people who naturalize to Japanese are required to legally give up their previous nationalities prior or instantly/automatically  upon receiving Japanese nationality: this vast majority being the Chinese (both PRC & ROC ) and the Koreans (both ROK & DPRK ). Even applicants from the G-7 country of the United Kingdom are required to lose their nationality prior to naturalizing. If one is required to lose their nationality prior to receiving Japanese nat...