FYI, yen is best purchased IN Japan. If you didn't know this already, I just exploded your brain with this little info-bomb.
Now, before we go any further, know that I'm not a finance maven. I don't study economy or work in banking and most of this is simply just information I've gathered over the years to try to obtain a better rate for my own trips. If you have any tips or tricks to add, please don't hesitate to comment! The finance landscape is changing fast and some of the options I've mentioned didn't even exist 2 years ago and I've no doubt that new options will appear in the near future.