From Halopedia, the Halo wiki
The Accord harness bears notable design influences taken from human iconography, such as Valkyries from the ancient Norse religion.
The Accord harness is unlockable as an armor permutation for Elite characters in Halo 3, exclusively as part of Season 7: Elite. It was one of a number of Sangheili harnesses intended to appear in Halo Online, appearing in the game files under the name of "Cerronsi".
List of appearances