Half of Roxas’s dual set of Keyblades alongside the Oblivion, and was transformed from his original Kingdom Key after he absorbed Xion. Fundamentally, the Oathkeeper is symbolic of Sora's memories of Kairi.
The Oathkeeper is formed when Sora uses Kairi's Wayfinder as a Keychain. After rescuing her from Hollow Bastion in Kingdom Hearts, Kairi gives him the charm for luck in the Secret Waterway in Traverse Town.
