Are you think Japan now bitcoin world leader ?
It is true that Japan has already given out license to CoinCheck as the first regulated and licensed cryto currency exchange. But the volume is still less from Japan. The crypto population of China is superior in number as well as in volume. So I doubt Japan is a world leader in volume. However, it has taken the first step to legalize something for crypto currency, so they are definitely a leader in the progressive decisions. But recently I have seen a news that China is now all set to give out license to some crypto currency exchanges which will be regulated under strict AML laws.