I first saw Tokyo Banana in Tokyo Station when I was heading to Shikoku to visit friends. A few years later one of my coworkers brought me back a box. I shared them with my classmates and now they too are fans of the delicate dessert that is best described as a banana-flavored twinkie, but better. Even my former coworkers bring me boxes of Tokyo Banana when they return to DC on business trips.
There are a variety of other TB products, including a dark chocolate version filled with the banana cream, or sugar cookies shaped like bananas, but I prefer the original.
Individually wrapped, they're perishable and should be consumed within a week.
However, I have never had a package that lasted that long.