For those who have not completed Xenoblade Chronicles 2, this page may contain spoilers regarding the plot. Discretion is advised.
The Omega Fetter is an object in Xenoblade Chronicles 2. It is a royal artifact guarded by the royal family of the Kingdom of Tantal, and is located at Genbu Crown. It takes the appearance of a glowing blue cube, normally encased in a golden metal sphere.
The Omega Fetter was originally a conduit used to communicate with and control Ophion, an Artifice of the Aegis. Ophion's orders were to protect the World Tree from any travelers, and it created the Great Void to do so.
When the ether accelerator is fired at Pyra, Genbu goes out of control and begins to dive beneath the Cloud Sea, threatening to crush itself and everyone within it with the pressure. The party travels to its head, where they find the Omega Fetter, where they find it has taken the appearance of a pulsing red crystal. Mythra is able to repair the crystal, and Pandoria tells Genbu to rise back up out of the Cloud Sea.
Soon after the party are attacked by Torna who manage to steal the Omega Fetter and escape with Pyra. When the party follows them to the Cliffs of Morytha, Malos uses the Omega Fetter to call upon the power of Ophion, however it is defeated by Pyra and Mythra's own Artifice Siren.