Spending the next six years out of Japan will do the trick. Then you can come back to enjoy four years of non-resident status for tax purposes. And yes, now when they have automatic information transfer agreements between the countries there is a real chance they take notice. It used to be that if they wanted to know your financial information like bank accounts they would need to send an inquiry to your home country. Now they just have to go clickety-click on their computer. (Details may vary, all pictures shown are for illustration purposes only).
And as
@warubuta said the 50 million limit is a totally different thing; that's for assets abroad, all income needs to be reported and taxes paid with no lower limits.
There are various interesting holes you need to avoid falling to also; for example if you trade stocks in the US of A and let's say you lose 10 million in one trade and gain 10 million in another. Now that is +-0 for you, right? Not so fast; the Japanese tax man doesn't count losses made through foreign brokers. So now you have 10 million of gains you need to pay the tax.
Similarly with the assets; if you borrow 50 million to buy a house abroad the Japanese tax man now thinks you have 50 million in assets and you need to report it.
The exit tax then concerns only Japanese citizens and permanent residents; and it kicks in only after you have 100 million in assets and have lived in Japan for five years. If you do and want to avoid it you still have until next year to skip out of the country as the law came in to effect in 2015.
Disclaimer: anyone taking any of the above as financial advice needs to get his head examined. Seriously. However if the information is useful to you blowjobs will be accepted as tokens of appreciation.