- "Memories of loss and dreams of vengeance, sealed in steel and composites. Mythic Shotgun with increased damage, accuracy, and rate of fire. The user's movement speed is also increased while Oathsworn is equipped."
- — In-game description.
The Oathsworn is an example of personalized equipment utilized by the Spartan-II's. It is a weapon that is often abandoned on the battleground over the years it was created, only to be recreated in preparation for another mission.
Every version of the weapon is slightly different, but the design of patterns on it has remained the same though for years since its inception. 
October 2558 Oathsworn
The Oathsworn is a mythic weapon in Halo 5: Guardians. As a slightly upgraded version of the Lawgiver, the Oathsworn has increased damage, accuracy, and rate of fire compared to the normal shotgun, features slightly more range and accuracy over the Lawgiver, and increases the user's movement speed while the weapon is equipped. As the weapon has a built-in Speed Boost, users of Oathsworn receive white auras and highlights.
In the campaign, the Oathsworn can be equipped only if Kelly is selected by a player in cooperative play. Because of this, the Oathsworn is the only special weapon in the game that cannot be equipped in the solo campaign. The campaign rendition of the Oathsworn has the Speed Boost removed and is exactly identical performance-wise to a standard Shotgun, including the strong vertical recoil.
- The rabbit painted on the side of the shotgun is a reference to Kelly-087's nickname, Rabbit.
- Near the trigger, the words "REMEMBER REACH" are etched onto the weapon.
Oathsworn in Halo: The Fall of Reach - The Animated Series.
First-person view of Oathsworn by Fred-104 in the Halo 5: Guardians campaign. Note the absence of the Speed Boost.
First-person view of Oathsworn on The Rig in Halo 5: Guardians.
List of appearances
- Halo: The Fall of Reach - The Animated Series (First appearance)
- Halo 5: Guardians
- Halo: Official Spartan Field Manual
- Halo: Lone Wolf