I have a Japanese account and continued to use it while I lived outside of Japan for a while, so it is not a problem to actually play.

You will need to find a way to continue to pay for your service or buy Crysta through a Japanese payment method, such as a Japanese credit card or buying game cards in Japan. Unless something has changed recently, they will not let you transfer your character to another region's account, nor will they accept payment from a non-Japanese payment method (like a foreign credit card).