I think it's Japan because it is also believed that it's the country where Satoshi Nakamoto lives or originated. Even if Japan is already a 1st class country with the love of technology, still they utilize bitcoin and even testified that their economic status is getting even better since they embraced the said technology.
Yeah Japan is the land of technologies then now they can forget about bitcoin, I think bitcoin is the best currency which gives good output to any country and thats the reason any almost everyone is now accepting the power of bitcoin, same as Japan, now china, Philippines and a lot of more countries are taking step ahead to bitcoin so I think now almost 90% of well developed Asian countries are switching to bitcoin,