While many shipping/moving companies exist to transport your belongings from the US to Japan, the company that my predecessors and I used is Nippon Express. My experience with this company has been phenomenal. They initially sent a person to give me an estimate about 2-3 months before I moved. They left some heavy-duty moving boxes for me at that time too.
At another date, they came and picked up my boxes and gave me specific instructions on how to clear Japanese customs when I arrived in the Japanese airport with my unaccompanied boxes.
In details, on arrival to the Immigration counter at the Japanese airport, I had to fill in 2 copies of the Customs Declaration Form stating how many unaccompanied boxes I had via Nippon Express. After clearing Japanese customs, they kept one of the Customs Declaration Form while they returned the other copy that they had stamped to me. Taking this stamped copy, I then went to the “abc” counter where they kept the stamped Customs Declaration Form and helped me fill out yet another form to have my boxes delivered to my new address in Japan. (Sounds complicated, but it really wasn’t bad).
I had 1 box that I sent via air shipment that arrived in 2 weeks after it was picked up. The other boxes (which there were many given my penchant for clothes, shoes, and accessories) were sent via ocean cargo that was delivered after 8 weeks.
On arrival of my boxes, I was astounded! After traveling for 2 months across the ocean and world, my boxes still looked brand new! My shipment was in better condition moving across the world than it would be if I moved across town in the US. Gotta love them Japanese service!