The size of taxes, of course, is impressive. However, it should be borne in mind that with small profits and tax deductions will be small. A little more than half of the profits are taken as taxes only if the profit is more than 367,000 dollars. I do not even know who can have such a big profit.
I think you shouldn't underestimate the amount of cryptocurrency millionaires that are actively trading. So for them it's easier to net $367,000 in profits annually since their initial investment capacity is a lot bigger. Of course this will target the people who are already rich but u think 55% is a little too much.
This will likely cause a massive tax evasion in the future. I don't mean anything outright illegal but rather something more like the "loopholes" people are discussing here. For example, you can become a tax resident of a country which has a soft tax regime in respect to cryptocurrencies (countries like Italy or Denmark) and officially pay (or not pay) your Bitcoin capital gains taxes there, thus avoiding paying the same taxes in Japan. Though I don't know if Japan has double-tax agreements with these countries.