IT depends how it compares with capital gain and income tax in the country in general, and how they handle losses. Also depends when they calculate capital gain (at the moment of conversion to JPY, or each conversion between different cryptos).

55% on insane free money this year would have been just fine. it won't be fine when (if) crypto ever stabilizes. there again, it's early days, and governments will need some time to tune things.

the clearer the regulations the better.