You, unfortunately, are not able to gain Japanese citizenship only on the grounds of heritage. However, you will be entitled to an application for naturalization to Japanese after a 5-year legal stay as a fourth generation Japanese. You can apply for a designated activity status under your heritage. Unfortunately, you cannot acquire Japanese citizenship on the grounds of pedigree alone. However, after staying legally for five years as a fourth-generation Japanese, you will be given the right to apply for naturalization as a Japanese. Since your great-grandmother is Japanese, you can apply for a designated activity status.
