How do you get it? It's well known, but here goes: you first need a Diamond Armlet. To get it, go to the small closed zone in Westersand, where you pick up Wind Globe for the Earth Tyrant quest. The chest is one-time only, and has 25% spawn rate. Once it spawns, you'll get Diamond Armlet 100% of the time. Next, ride a sky ferry from Rabanastre to Nalbina(or vice versa). On the uppermost deck is a treasure chest with 1% spawn rate. However, even if it spawns, it's INVISIBLE, and it won't make the noise a chest makes when you get near it. However, since the chest is physical you won't be able to walk over it, so if you try to walk over it it'll seem as if an invisible wall is blocking Vaan from going any further. If that happens, that means the treasure have spawned. You can refer to any video on YouTube that shows the precise location. I repeat, it spawns on the uppermost deck, at the farthest center(right below the large blue propeller in the middle). Once you realize it spawns, EQUIP DIAMOND ARMLET ON "VAAN" and open it. There is 1% chance it holds Zeitengrate. So every time you enter, the probability you'll get the bow is 0.01%, or 1 out of 10,000. AND THIS IS THE ONLY WAY TO GET THIS UBER-WEAPON.