[Baltan II]

So it's sitting in an American customs office? Then you'll want to contact the post office first. Bring something that verifies your order with Mandarake as well as your tracking number and explain the situation to them. Also shoot Mandarake about an email. They're not going to be able to do anything for you in Japan necessarily, but the post office might need them to verify your order and address, or something. Also, doing so is important in case the second-worst thing happens and your package is returned to sender.

The worst, obviously, being your package getting stuck in limbo, but the fact that you have tracking should mean the chances of that happening are low.