Transforming your iPad/iPhone into a register is also pretty neat. I wonder if they'll look into putting an NFC reader in there and interface with all the IC cards here. Most people don't pay for their coffee by credit card.
There have are some Japanese startups, such as Coiney (http://coiney.com/) who are already doing the same thing as Square.
We run a casual, low-pressure mixer kind of event about once a month. If you come to Japan, you can follow our blog (http://www.makeleaps.jp/blog/en/) or signup on Doorkeeper to get notified of events. We get lots of visitors from abroad swinging through and we're always looking to help support other startups in Japan or small businesses trying to enter the market here. It's a really good crowd of people.
There's also a meetup for HN readers in the kansai area of Japan if you're visiting there.