As was my experience as well; everywhere I go in Japan, the receipt has always been in JPY.

As an additional side point, if one can read Japanese, even that Japanese acquirer for online businesses that I posted above doesn't really state any benefit to merchants; it only says "it'll be a service to your customers who would like to see the amount in their home currency without currency fluctuations. By providing this service, foreigners will more likely shop at your place than your competitors!"

Nothing about "businesses earn additional revenue from conversion fees" is noted in that Japanese acquirer website, which is what other countries' acquirers use to market pitch DCCs to merchants. (i.e. FirstData's DCC sales pitch to US merchants)

Either Japanese online business acquirers are trying to pocket the difference by collecting the currency fees for themselves or, Japanese online business acquirers themselves don't know what DCC is yet or haven't really looked into what it really does to market it that way to benefit Japanese merchants.

The American skeptic in me would say the former. Yet the Japanese in me wouldn't be surprised if it's the latter. I'd even say this as an American of Japanese descent - the Japanese people are really bad at marketing. They make great products, they suck at marketing.