In October 2558, Fireteam Osiris deployed to Sanghelios after learning that a Guardian was there. Realizing that it was in Sunaion, Osiris enlisted the help of the Arbiter Thel 'Vadam and the Swords of Sanghelios to assist in getting to it.
The Swords of Sanghelios attacked Sunaion, Jul Mdama's Covenant's final major stronghold, they sent in various warships, Liches and Phantoms. FireteamOsiris was deployed to the city in the midst of the battle by Thel 'Vadam's Lich. Osiris and Thel's forces engaged Jul's Covenant on the ground, while Jul's Covenant and Swords of Sanghelios ships fought in the skies. Osiris was able to eliminate several Anti-air guns allowing more Swords of Sanghelios forces to land. Osiris then moved to the lower levels of the city as Promethean forces joined the battle on the upper levels. Osiris engaged more of Jul's Covenant and made their way back to the upper levels as the Guardian awakened. Osiris and Thel then engaged Warden Eternal, after defeating him Osiris headed towards the Guardian while the Swords of Sanghelios wiped out the remaining Covenant forces.