This actually worries me a some. If the BOJ supports a crypto coin that is pegged to the yen, then the BOJ is actually staking its credibility on that peg. The BOJ will have to defend that peg, bidding into weakness and selling into strength in sufficient amounts to maintain parity. Maintaining a peg has a real cost - sometimes central banks have to absorb huge losses to maintain currency pegs. If bitcoin and the other alt coins are freely traded in Japan, they provide a easy way for individuals to scape the j-coin and drive up the cost of the BOJ's defense of the j-coin during times of trouble. Would it not be easier for Japan to make it much harder to trade in other cryptos? Particularly in times of trouble when the j-coin needs support? Seems like the j-coin could create an incentive for Japan to come down hard on cryptos.