Kitun 'Arach was born in an unknown keep on Sanghelios. As a child, Kitun was very close with his brother Jacul - with the two spending their time together in studying, hunting and combat training. Both Sangheili presumably served in the Covenant military during the Human-Covenant war, but following the conclusion of the war in 2552, Kitun was left disillusioned and alone while his brother returned to Sanghelios and swore fealty to Thel 'Vadam's Swords of Sanghelios. Unable to reconcile himself to 'Vadam's peace treaty with humanity, Kitun eventually joined Jul 'Mdama's Covenant, where his skill as a warrior soon led to his promotion to the role of commander. Following the deaths of Parg Vol and Gek 'Lhar during the Second Battle of Requiem, Kitun rose to become one of Jul 'Mdama's lieutenants, but while Kitun remained fiercely loyal to the Covenant's ideology during this time, he began to feel disdainful of 'Mdama's leadership and secretly considered his superior to be a fool. Kitun was present on the surface during the Battle of Kamchatka, where he personally led troops in battle against Promethean forces. During the battle, Kitun briefly and unofficially allied with Fireteam Osiris to defeat a contingent of Promethean Soldiers which managed to drive off one of 'Mdama's Krakens. Somehow, Kitun managed to escape Kamchatka with a considerable force of Covenant troops and made his way to Sanghelios, where a detachment of Covenant forces had been locked in conflict with Thel 'Vadam's army for some time. With the death of Jul 'Mdama, Kitun and several of Jul 'Mdama's former lieutenants assumed joint control of remaining Covenant forces and coordinated a final assault on the Arbiter from the holy city of Sunaion. Once again thrust into direct contact with the Swords of Sanghelios, Kitun recorded several messages and sent them to his brother, Jacul, imploring his distanced sibling to come to Sunaion and join the Covenant. Jacul responded with a handful of messages of his own, stating that he held his brother no ill will, but that he believed it was a blemish upon a Sangheili's honor to continue to fight in the name of the Covenant following the Great Schism. When the Battle of Sunaion finally came, Kitun found his brother in the undercity and dueled him. Although Kitun would slay Jacul outright, he was himself grievously injured by his brother's energy sword and died shortly before the awakening of the Sunaion Guardian.
- Kitun 'Arach can be killed in Osiris, however his messages to Jacul 'Arach may still be found later in the game.