From Halopedia, the Halo wiki
Fractured Ward was created to aid warriors on the battlefield, as well as to defend and protect sapient lifeforms. While assisting in the defense of a vital teleportation array, Fractured Ward was thought lost in the facility's catastrophic destruction.
The battle against Gargos in the Killer Instinct Universe has widened the cracks between worlds, releasing Fractured Ward from eons of lonely wandering in a crumbling refuge hidden between dimensions. Fractured Ward identified Earth's heroes and works with them to heal breaches in reality caused by demonic incursions.
Behind the scenes
Fractured Ward is a character created specifically to serve as a "Guardian" for Killer Instinct's Shadow Lords gamemode. In gameplay, Fractured Ward provides the player with extra layers of defense to protect them against Gargos, the primary antagonist of Killer Instinct.