Great answers by Dick Karp and David LaSpina.I can only add my two cents of knowledge to their insights.The first thing: citizenship and naturalization are two different matters.You can only get citizenship if you were born from Japanese parents, AND being registered within 3 months with your local Japanese consulate.AND when you reach 20 years old, it's mandatory you choose whether lose your local citizenship or your Japanese citizenship.Should you not make a move, you lose your Japanese one by default.On the other hand, you might be naturalised Japanese (i.e.: become a non-born Japanese with a permanent visa) if all these criteria are met:- you're living for at least 5 years in Japan- you're at least 20 years old- you can read, write and speak Japanese fluently- you are willing to go through writing exams and interview processes- you have professional skills and $ to support yourselfEvery case is examined and weighed individually. Say, if one of your parents is Japanese (Japanese-born), the Ministry of Justice may wave the age and residence requirements. But again: it is a case-by-case process.Sources:Japanese nationality lawI want to become a Japanese nationalMany angles to acquiring Japanese citizenship | The Japan TimesAlso, I went myself to my local Japan consulate and talked with them.