This product was mentioned in
with an average of
"Any fixed knife containing a blade length of 15 cm or more requires permission from the prefectural public safety commission in order to possess. Permission requirements also apply to any type of pocket knife over 6 cm (including Automatic Knives), spears over 15 cm in blade length, and Japanese halberds. All knives with a blade length over 6 cm are prohibited from being carried, under a crime law, with an exception for carrying for duty or other justifiable reasons. There is a penalty of up to 2 years prison or up to a ¥300000 yen fine."
It sounds like if you are exploring the island the maximum you can carry is 6cm folding knife.
With that in mind what about The spyderco squeak
or the dragonfly
or the recon micro
Spyderco Squeak. Great steel; great ergonomics; great little knife. [link]
I believe there are not many (if any) places in the world this would not be legal. [link]