The victory of Republican presidential nominee Donald Trump invoked memories of June's Brexit vote, a reminder that the unexpected can always happen.

For Japan, a Trump presidency could mean more headaches, as he is new to politics, to say nothing of diplomatic expertise. In essence, the billionaire businessman represents uncharted waters, a situation that could undermine the Japan-U.S. alliance and upend regional security in Asia.

"It's a complete mystery to me what his Asia policy is going to be. He lacks experience, he does not understand the subtlety and complexity of the regional picture," said Andrew Nathan, professor of political science at Columbia University.