Merril:

They have baggage shippers right in the airport at Narita. I think it makes sense to land in Tokyo, ship most of your bags to Osaka (either hotel where you will be staying or ship's representative) and then take the Limousine Bus into your Tokyo Hotel. When it is time to go to Osaka, just take a cab to train station and then catch bullet train to Osaka.

Another option is to take all of your bags on limousine bus to hotel (we will see what this is like with six suitcases next week) and then ship from hotel day before you depart for Osaka.