I've non-revved all over asia (China, Japan, Malaysia, Singapore, Thailand, Vietnam) and I cannot recall ever being asked about a return ticket. I have both visited and transited through Japan. I found it extremely effecient and I never had any holdups with customs/immigration.

Even when I showed up in Sydney and Auckland with my arm immobilized in a sling, nobody said one word about my condition. Good times!

Having said that I'd better print out something on my next trip.