Naturally there are spoilers ahead for the Bow upgrade, so be wary if you don't want to know what it is or how items are upgraded to begin with. One really awesome feature in Skyward Sword was the fact you could upgrade your items throughout the game in a bit of RPG like action. In fact, we detail this in our Skyward Sword Walkthrough. As it turns out, item upgrades are also a real deal in A Link Between Worlds as well -- something we just learned from Eiji Aonuma's panel at Comic Con. While the details are sparse on everything we would like to know about upgrading them... we still have a few details, including what the Bow upgrade does!
So as far as we know, you return "Maimai's" to Mother Mainai in order to upgrade your items. Obviously those spellings are not official, but are the best we could find in terms of understanding what was said. In addition, the Bow upgrade causes the item to fire three arrows at once, which will undoubtedly be useful when the stuff on screen gets a little crazy. I would also presume this uses more of the stamina meter, but I can't confirm that at this time. Stay tuned as more details are seemingly hitting us every few minutes! Be sure to bookmark our A Link Between Worlds Walkthrough!