If you're playing Bravely Default--and you should be, as we described in our review--you've likely run into some chests. Red ones work like you'd expect, opening when you walk up to them and giving you random items. Blue chests? Well, they're locked, and despite what you might think, you can't open them once you get the Thief class (and they're not linked to microtransactions, either). So, how do you open them?
You wait. You wait for a long time. These chests aren't waiting for you to get some new ability, they're tied to the end-game of Bravely Default, and that doesn't start until Chapter 6. Then, you'll find the Treasure Chest Key on a ship, and you can use it to roam around the world, cracking open Blue chests and gaining access to the best items in the game. It's a wait, sure, but it's absolutely worth it, and there's nothing you can do about them before that.