You are required to have a valid visa (Status of Residence) from the Immigration Bureau of Japan at the time of application and you must have been living in Japan for at least 5 years. Also the bureau... confirms whether you have been living in Japan at least 80% of the 365 days every year. The time spent on a Student visa cannot be counted in this 5 year period. If you get a Japanese passport, you have to give up your other nationality (according to Japanese law, you can only hold one nationality)