Originally Posted by
5khours
That is for naturalization. The situation is different for kids born into dual nationality.
Oh, apologies.
It still depends on your other nationality, though. At the very least you have to tell the Japanese government that you hereby renounce the other nationality, which may or may not be a valid renunciation from the other country's perspective. The US won't recognize such a statement, but other countries may (I believe that most East Asian countries will).