Completing the quest Divine Might will simultaneously complete this mission, and it has additional rewards.
After arriving in Ru'Aun Gardens take the center portal to the main island. Travel straight to the center of the island.
Be careful not to stray from the middle path, for the Groundskeepers along the walls on the blue pads are aggressive to magic, as per usual, but in addition, all Groundskeepers in the area that are standing still near a blue pad are aggressive via sight as well.
In the Shrine of Ru'Avitau, continue straight until you find an unmarked target on the wall. Examine it to receive a cutscene.
If you intend to do Divine Might click the point again once the first cutscene completes to flag Divine Might so you can get your Ark Pentasphere. See the Divine Might page for information about the mini quest.
If you do not get this cutscene, you can still do the fight, but you will not be credited for it for this mission.
Warps around the circular area of the Battlefield, except during Blood Weapon, when it will follow the current target. Does not follow up the stairs (except during Blood Weapon, most likely).
Tips & Tricks - Mages stand at the stairs and attack/heal from there as the AoE attack can be deadly. Damage dealers simply melee. Shadow Images are very useful to evade most spells as AoE ones are not used that often.
Tips & Tricks - Sleep the pet and focus on Ark Angel MR. The one having most enmity at the time, will be charmed so plan accordingly (you will get charmed even if the pet is still alive). She does not wait to use Charm, so if you are out of range at the time, you'll avoid it.