They will, have to, in the future 
Why? What regulation is necessary that doesn't already exist?
However, the opinion on bitcoin within the Japanese government appears to be split. They have also talked about taxing bitcoin transactions. That sounds like a recipe for destroying bitcoin.
For example, in order to finance the American Civil War, the Lincoln administration issued a fiat currency called "Greenbacks" (printed in green on one side) . At the time, mainly different kinds of bank notes issued by a large number of state banks were in circulation. By assessing a 10% tax on all transactions using bank notes, Lincoln's Treasury Dept. successfully forced the state banks to stop issuing bank notes, as they became prohibitively expensive to use in transactions.
Taxation could have the same kind of negative effects on bitcoin.