You dont get my point here. Japan accepted Bitcoin and not all crypto currencies as legal payment method. The article you linked also states exactly what I said.
Quote: Japan announced on Friday that bitcoin would be accepted as a legal payment method beginning on April 1, 2017.
Not all crypto currencies in general. Also not Mona as far as I can tell, therefore I asked this question in the first place. If Japan would give Mona the same status as Bitcoin already has there, it would likely have a huge effect on its price. As it was the case with BTC. As I can see from the other link you provided, its already being adopted from more and more merchants, this is certainly a step towards this, there is only the official announcement of it missing.
My friend, all cryptos are legal tender in Japan.
Find a Japanese friend that will find an article in Japanese for you.
As you read, MONA is accepted by merchants. So it means they are allowed to.
Most popular coins there are BTC, MONA and NEM.
Since transaction costs are high in BTC and since NEM POI algo is very questionable, there is good chance that MONA grows rapidly.