Having dealt with dozens of personal F/X transactions for JPY/USD as a way of getting money from Japan to the US, I can categorically state that the TC F/X rate is the best all-in rate (including fees and spreads) of all the other alternatives, including ATMs, credit cards, and even wire transfers.

Frankly, I don't know if this applies the other way (for bringing money into Japan), but if it works the same way, the idea would be to buy JPY T/Cs abroad and then exchange them all for cash upon arrival, and use that cash as spending money for day to day items.