Self explanatory title! If your dog is arriving in the US as cargo (unaccompanied through the cargo terminal) you are now required to hire a customs broker to clear the dog through customs on arrival. I just found out the hard way, and a dog had to sit in the cargo terminal for an extra couple hours while a broker was found.
A google search for a customs broker will generally bring up a few, and expect to pay a bit for the service. I've heard of a quote for 300USD.
I will now be contacting the shipping agents and airlines on the Japan side to complain that they are not making this information available to dog owners.