Enemy of my Enemy

Enemy of my Enemy is an achievement in Halo 5: Guardians, awarded for protecting Kitun 'Arach, the Sangheili Warrior attacking a hill in the level Osiris.

Description
After passing through the Forerunner security station and a cave, the player(s) will come to a hill being defended by Promethean Soldiers and Crawlers, and assaulted by a small group of Covenant while a Kraken attacks from a distance. The Covenant lance is led by a single Warrior, who must be protected and kept alive. The achievement is earned when he steps onto the platform at the top of the hill.

If the Elite spots the player or their allies, it will attack them. It is recommended that the player attempt this achievement on co-op, as the NPC members of Fireteam Osiris will also attack the Elite. But once the Elite reaches the top, he will become an ally and fight alongside Osiris. After that he will no longer attack the player or their teammates, but will stay at the platform and not accompany them further in the level.