Even if you're thinking of packing the sword up and sending it as checked luggage, you should be aware of the airport entry inspection at NRT:

There is a security check on the way into NRT. They mostly just look at your passport and wave you through. However, if you are carrying something that looks like it may be a sword or knife, they will want to take a look at it. And they will confiscate any swords or knife before you enter the airport.

Back in the late '80s or early '90s, I sat next to someone on a flight out of NRT who had purchased a large chef's knife in Tokyo. It was taken from him by the security guards who saw it as he was going into the airport. During the flight, the FA returned the knife to him. (I remember wishing that they had waited until we were disembarking before handing him that knife).

Therefore - if you're planning to pack up the sword and send it as checked luggage, I would make sure that it doesn't look just like a sword in bubble wrap. Using a box would be a good idea.