Emperor Akihito's reported intention to abdicate in a few years because of his advanced age has shocked the nation, made headlines and triggered discussion among intellectuals on how the Imperial throne should be succeeded.

But since the first report surfaced earlier this month, Imperial family members, including the Emperor, have remained mum. Prime Minister Shinzo Abe also declined comment, citing the "sensitive nature of the issue."

So what, exactly, is politically sensitive? And what legal and constitutional issues are involved if an emperor abdicates?