It's already been spoiled alittle bit the Producer Live letter, and in the video.

The large sword that hit the ground, I bet will be in the fight with Bahamut. If it is, we will need to pray to it to help defeat Bahamut. Why pray? The video shows them rising back up after Y'shtola, Thancred, Papalymo, and Yda prayed at the shrines.

It will mostly likely cause an anmesia effect on him with a gravity effect.