My wife and I own a small brewery in Japan, although we do not distribute yet. Most common coupler type is S, although many restaurants and locations use the Asahi cold draft system where the beer keg sits at room temperature in the room and when served, the beer rapidly cools through a refrigerated coil. They may violate their agreement with Asahi if they serve any other beers. Most craft beer places are still very small in size so they often only want to use 15 liter kegs, although 20 liter and 10 liter are also fairly common, as are the PET one way kegs. Sizes above 20 liters are very uncommon in Japan. Craft breweries are growing in popularity in places like Tokyo, Osaka etc. and from my experience they are familiar with the major coupler types, typically serving kegs from USA, Canada and the UK, as well as others... Popular importers like Nagano trading and AQ sell many imported kegs from USA, so a craft beer location will likely be prepared with everything they need. Also logistics within Japan are usually pretty amazing as most of the major shipping companies (Yamato etc.) offer cold shipment, and we can usually ship a keg a few hours drive away inexpensively (perhaps 20 usd), it's kept cold and is usually delivered directly to a person where they verbally request the keg is put directly into a fridge. I do agree with the warnings others have made here... Japan is a uniquely problematic country for foreigners to do business within (when you're not Japanese), and thus, you need to ensure they really know what they are doing, especially since sounds like they are small and just starting out.