Comment by 29J

From some reading up, you've lost nothing by not pursuing yet. Japan's Civil Rehabilitation Act requires the funds belonging to unclaimed accounts to be preserved and eventually deposited with the court, instead of being shared amongst other creditors. There is likely an internal placeholder claim number holding the proper amount waiting for you to convincingly attach your name to it. This is the world of law not programming, so I wouldn't let forgotten passwords or closed email accounts deter me if I were you.