My wife and I just successfully exported a Edo-era Katana and a Muromachi-era Wakizashi - both bought in Japan - via a checked suitcase on a United Airlines flight from Sapporo to the United States (via Tokyo). We were extremely nervous, did a lot of research in advance, and wanted to share our experience. Sharing in case this helps others.
First off, we purchased a padded gun case with heavy duty TSA pad locks to transport the two swords. This ¥24,000 that we spent on the hard case was a wonderful investment. I highly recommend Lykus brand suitcases for this purpose.
Secondly, we live in Japan and processed the entire Export Certification process ourselves. If you don’t speak Japanese, or don’t live
in Japan, I would highly recommend using a private service in Japan for obtaining the export certificate (most Japanese sellers seem to include this in the price of the sword). Other private companies offer export certification services (even if you don’t buy the blades from them). Doing it ourselves took six weeks from submission to receiving the certification. Written Japanese language proficiency was necessary.
Other lessons learned:
(1) Departing from a city other than Tokyo or Osaka made things a bit more difficult. The Sapporo check-in agents were unfamiliar with nihonto export procedures and required that we have our suitcase reexamined in Tokyo.
(2) The export process in Tokyo involved two customs agents and a police officer inspecting the blades and export certification. My personal details, including residence card and passport, were copied. They applied a magnet to the blades to confirm that they were made of iron. The whole process took about 45 minutes. Bottom line: Budget extra time if traveling with nihonto.
(3) Customs in Tokyo kept the original export certificate. Make a copy.
(4) I was also traveling with some expensive tsuba and spare antique sword parts. We did not obtain export certificates for the tsuba. Customs did not think twice about tsuba or any of the other sword parts we traveled with. It remains unclear to me if tsuba require export certification procedures.
(5) Fearing theft, I packed both wrapped blades with discreetly hidden Apple AirTags. These gave me peace of mind, but may have not been necessary.
Good luck to those traveling from Japan with Nihonto!