Originally Posted by
Ultimatecalibur
A bunch of sky pirates stumbled upon an attempt by a powerful voidsent to unseal an even more powerful one. It tied heavily into the War of the Magi plotline that is core to the White Mage, Black Mage, Scholar and Red Mage job stories and a number of dungeons (Adampor Keep, Lost City of Adampor, and Wanderer's Palace).
Crystal Tower was more or less a tangental sidequest until ShB brought it into the main story so they could easily make it required and relevant in several ways.