When I travel abroad, it's natural that I can draw cache from ATM by credit card in 24 hours. It's good to carry cache from Japan for a short trip considering the rate, and traveler's checks for a long trip considering a safety, but ATM is also convenient. Several times, I have helped by the ATM. In Japan, it was terrible, but in recent years it is available until late at night, and there is ATM in a convenience store, I think it is better now.
However, I surprised that most of ATM doesn't accept credit cards issued overseas for caching. For foreign visitors, It's very inconvenient.
FAQ page of Japan National Tourism Organization's official guide, FAQ - Visiting Japan describes:
More than 26,000 Post Office ATMs exist at various locations throughout Japan, and stickers indicate whether a Post Office has an ATM machine. Cirrus, Plus, Maestro and Visa Electron networks are accepted, as are Visa, MasterCard, American Express and Diners Club credit cards.
In July 2007, ATM in Seven-Eleven convenience store start to accept credit card issued abroad for caching, so Seven-Eleven is good place for caching.