As a descendant of a Japanese citizen, you can obtain a status of residence, and after living in Japan for a certain period of time, you can apply for Japanese nationality. Unfortunately, there is no way to recover Japanese nationality from overseas.
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How can I apply for citizenship by descent in Japan?
My grandmother is Japanese, but she emigrated to Korea when she was young and had my father with a Korean husband and never renewed her Japanese documents after turning 32. My dad passed shortly after having me and didn't get to apply for Japanese citizenship. Do I have right/route to claim Japanese citizenship?