Tatuo, there are some tips for your test run.
Even an Indian cheap khukuri is a part of limited resources on the earth, and it's vicious to give in to customs where no recycling is considered.
End of Dec, and early Jan fit your puropose as customs are busy with horde of people at every airport.
Customs does not xray all the baggage. They look at faces of passengers for clues of smuggling. Be sure a khukuri is legal in Japan because its true. Only there are some customs of different thought against legal basis, and only there are no way to get over them in non-democratic country. Keep innocent looking all the time, get surprised if they find the khukuri to tell you it's not legal, and ask them why calmly because you heard a khukuri is a kind of hatchet from Japanese friend. You don't have say it was a wrong_friend.
Hope your success to save resource.
------------------
Did you enjoy today?
\(^o^)/ Mizutani Satoshi \(^o^)/