- “Now take this sword, this Treaty-Blade. Occurian seal, mark of your worth. Cut deep the Cryst and seize your Shards. Wield Dynast King's power! Destroy Venat!”
- —Gerun, leader of the Occuria
In the past, the Occuria gave a blade known as the Sword of Kings to King Raithwall who used it to carve the Dawn Shard, Midlight Shard, and Dusk Shard from the Sun-Cryst, and forge the Galtean Alliance. The Occuria gives the Treaty Blade to Princess Ashe, Raithwall's descendant, for a similar purpose: to cut her own shards from the Sun Cryst, and use them to destroy the Archadian Empire and Venat, rogue Occurian who has been teaching men how to manufacture their own nethicite. By this act Ashe would submit to Ivalice being controlled by an Occurian-appointed ruler, the destiny that the Archadians are trying to overturn.
Atop the Pharos at Ridorana Ashe is given the chance to cut new shards of nethicite from the Sun-Cryst, and use them to fight the Empire. However, she realizes the Dalmasca she is fighting to reclaim is one which does not abuse the nethicite's power. Ashe refuses the Occuria's assistance and does not use the blade.
Doctor Cid arrives and produces the three shards Raithwall had cut, returning them to the Sun-Cryst and causing a violent and volatile Mist to spill from the stone. Vaan wields the Treaty Blade while Ashe wields the Sword of Kings, and the two attempt to destroy the Sun-Cryst to stop the Mist. Reddas takes the Sword of Kings from Ashe and sacrifices himself to destroy the Sun-Cryst as the party escapes.
Unlike the Sword of Kings, the Treaty Blade is not lost and remains in the party's inventory.
The Treaty Blade is a two-handed Greatsword with an Attack power of 30 in the standard version and 67 in the International Zodiac Job System version, and boosts Evade by 30. It can't knockback opponents like other greatswords. In the standard version it is the Greatsword with the lowest attack, along with the Sword of Kings, but its combo rate is 25%. It requires no license to equip, and as a key item cannot be sold or discarded. All greatswords have 2.47s charge, and 1.2s action time, making them average what it comes to attacking speed.
In the quest "The Three Collectors", the Treaty-Blade is stolen from a collector named Durilda by a mysterious thief. Gilgamesh is falsely suspected.
Ashe wields the Treaty Blade in the Theatrhythm Final Fantasy.
- “Symbol of a sworn treaty, and the irony of bringing about peace through destruction.”
Treaty-Blade grants +4 to Attack. It can be equipped by Knight, Mystic Knight, Cecil, Bartz, Cloud, Squall, Seifer, Steiner, and Vaan.
Ashe's Play Arts action figures includes the Treaty Blade.