Bravely Default: A stroke of genius (spoilers!)
Dubbed "Lying Airy", this ending is available from chapter 5 up until the awakening of the ultimate crystal in chapter 8 and must be triggered by disobeying Airy's instructions and shattering a crystal. This is achieved by keeping on pressing the x button after Airy orders you to stop doing so, and this maneuver can technically be performed on any crystal from chapter 5 onwards—although it's highly recommended to wait until chapter 7 or 8, since the time needed to shatter a crystal is directly tied to the strength of your party and thus to their levels.
The hint hidden in the title from chapter 6 onwards immediatetly comes to mind: what a brilliant way to hint at the truth, bound to either arouse suspicions or confirm them! Chapter 6 also sees the party mull over the situation and wonder whether waking up the crystals is the right thing to do, whether Airy may have ulterior motives and, most importantly, what would exactly happen if Agnès kept pouring energy into a crystal until it shattered instead of stopping doing so when Airy orders it. After that intense musing, they drop the subject and don't mention it anymore in subsequent chapters. I first deemed this a serious mishap, wondering why the story was not expanding on these suspicions; yet a mishap this is not, but rather a brilliant narrative device. The characters are not drawing conclusions from their abundant suspicions because it's up to the player to do so themselves and act accordingly, in a vertiginous display of free gaming will.
Link's Awakening, in which the player follows the instructions of a helpful mysterious creature before a bunch of hints arouses suspicions regarding the ultimate goal promoted by said mysterious creature, which may not be as wholesome as it seemed at first sight. The player can then exercise their free will and refuse to follow the creature's instructions in order not to trigger a dramatic outcome. However, that option is not a true choice but rather a defaulting of sorts that's not planned by the game; as such, it doesn't lead to a specific ending, but rather to an eternal statu quo. Bravely Default went much further than Link's Awakening and enriched the mix with a specific gameplay action and a dedicated ending, leading to a much more compelling result.
All in all, this alternative ending is absolutely brilliant, ingenious, clever and whatever synonyms you can think of, so much so that it pretty much single-handedly makes me forget the shortcomings of the narrative. I am utterly grateful to Bravely Default for having treated me to such an original, fresh and thrilling experience, and I can only hope that Bravely Second will have similar delightful surprises in store. Thanks for reading, and be my guest anytime!