Hi,
I took the liberty to copy from another site.
hope that it will make you think.
In the first place, I must declare that I'm not the author of the following info, I just made a compilation from this forum. But maybe it will help others you know?
"........ First of all, note that the age you must choose your nationality is 22. This is according to Article 14 where it says,
"A Japanese national having a foreign nationality shall choose either of the nationalities before he or she reaches twenty two years of age if he or she has acquired both nationalities on and before the day when he or she reaches twenty years of age or, within two years after the day when he or she acquired the second nationality if he or she acquired such nationality after the day when he or she reached twenty years of age." However, the law doesn't actually tell you to surrender your other nationality. It just says you have to keep trying. Please refer to Article 16 for details where it says, "A Japanese national who has made the declaration of choice shall endeavour to deprive himself or herself of the foreign nationality."
So bottom line, you won't get "caught" even if they find out you have dual nationality after 22 years of age. Just tell them, "I'm trying" and you'll be okay.
If the worst thing happens, remember any government cannot impound a travel document that belongs to another country. They can only "advise" you to do certain thing after entry.
No authority will punish you even if you continue to hold dual nationality of Japanese/ ... another Citizenship. Say you declare japanese nationality, and tell Japan you renounce your US, British, Brazilian or anyone.
Japanese government would like you to choose but they cannot compel you to do so simply because the US government/and other ones likewise, will not recognize their intention to force you to relinquish another citizenship. Basically, you are free to be a US citizen for as long as you choose to be one. Most countries do not accept renounciation done made to foreign governments. It is a loophole that Alberto Fujimori used. Now, anyone can use it.
They can't revoke your Japanese citizenship, as long as you got you Nihon passport. If you are in the States, or in any country, just go an renew your passport at the Japanese Embassy or Consulate. As said before, go with the parent that is a japanese national.........."
You will need a "jyuminhyo" at your parent's ward