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.
Completely wrong, my friend!!!
Japan is a leader in blockchain technology, but not the most developed country in the crytocurrency market.
New China is the country that holds the most bitcoin right now, new Chinese projects are always more popular than Japanese projects.