Once again we see the problem with only considering investments in purely yen terms. Anyone with this very narrow mindset of thinking about short term forex movements and who only see's things in the prism of yen based returns is going to severely limt their investment opportunties.
Much better to not have a 100% yen mindset and think of having JPY, USD, EUR, AUD or whatever investment buckets so you are not putting all your eggs into a JPY basket over the long term. None of us know what the yen exchange rate will be in 1, 3, 5, 10 or 30 years time.... don't miss out on investments because you're scared of exchange rate risk. Imagine how terrible a strategy that has been for the past fifty years.....