Was at least one of your parents a Japanese citizen at the time of your birth?

Japan uses a strict parent-only rule for citizenship by descent, there is no grandparent route, no great-grandparent route, and no broader ethnic connection claim. If neither of your parents held Japanese citizenship at the time you were born, the standard citizenship by descent pathway is not available to you. If one or both parents were Japanese citizens at your birth, regardless of how they became Japanese, you may qualify.