Originally Posted by jib71

AFAIK, there's no requirement for a passport. IIRC, I have flown on JAL and ANA domestically with no ID check at all, and as far as I can tell that's still the case. Individual airlines ID requirements may differ (e.g. low cost carriers do check ID, I hear). But I would expect all to be satisfied with a Japanese drivers license or other photo ID issued by Japanese government.