4 years of “College Student” VISA plus one year Working VISA apparently satisfies one of naturalization requirements, or residence requirement that an applicant must live in Japan more than 5 years consecutively.
However, actually it might be required that the applicant have worked for a certain period as a taxpayer. As a result, 4 years of “College Student” VISA plus one year Working VISA may not be long enough for naturalization permission.
It is recommended to consult with Legal Affairs Bureau or District Legal Affairs Bureau which is in charge of your residence area. Here is the list of them ( in Japanese ) on the web of the Ministry of Justice. You may have an impression that it is hard to consult with them, but they will answer you kindly. Probably they cannot simply answer “how many years of working VISA is needed.” But you should talk about details on your own situation.
Nationality Law Article 5 stipulates the following six requirements for Naturalization. But even though all of them are satisfied, it does not mean that the permission is automatically granted. Still the Minister of Justice has the authority to decide whether or not to grant the permission.
1) The person domiciled (lived) in Japan for five years or more consecutively.
2) The person is twenty years of age or more and of full legal capacity to act according to the law of his or her home country.
3) The person is of good conduct.
4) The person is able to secure a livelihood by one's own property or ability, or those of one's spouse or other relatives with whom one lives on common living expenses.
5) The person has no nationality, or the acquisition of Japanese nationality will result in the loss of foreign nationality.
6) The person has never plotted or advocated the overthrow of the Government of Japan.
And some of the above requirements can be exempted as simplified naturalization, typically when a foreign national get married with a Japanese.
Case 1 : After getting married with a Japanese, the applicant has lived in Japan for more than three years
Case 2: Three years have passed after their marriage, and the applicant has lived in Japan for more than one year.
In both cases, the above requirement 1) and 2) will be exempted.
* Reference Book (in Japanese)
“KIKA TETSUDUKI NO TEBIKI (A guidebook for naturalization procedures)”
(by YOKOO TSUGUHIKO & SHINOZAKI TETSUO) NIHON KAJO SHUPPAN
This book explains the details.
“KIKA SHINSEI MANUAL (A manual for naturalization application)”
(by MAEDA OSAMI) SUBARU SHA
This book is easy to understand.