I fly about once a month to someplace in the world (sometimes Japan sometimes other places) I almost alway take my boken, jo and my Iaito. I use a pair of 4" PVC tubes held together with Pipe clamps. I always tell them up front what's in the case and as of yet I haven't had a problem...I was in Guam for 9/11 and have flown though many many international airport with security way beyond that of US airports. Most Xray your stuff as it comes in and they are always more freaked about my Tool box that they are about my sword.
BTW Louis you are vetted so to speak so being in the military, you are indeed immune to many of the security events that others have to deal with. One of the may unseen pleasures of serving uncle sam I guess.
Also never carry fingernail clippers much less a pocket knife at Narita airport...Dont ask my why just take my word for it it's a very bad thing