if you have the watch shipped, you will have to pay the import duty and taxes in Japan. Than cannot be avoided. What you can do is to have the seller...underdeclare....the value of the watch and pay less.
Cheers - Sergio
So if it gets lost for some reason or a 5 finger discount happens at Customs, you'll be wishing you insured for full value since you were the one who told the seller to underdeclare.
Cheers,
Anthony