Religion plays a huge role in the world of Diablo 4, as light and dark are constantly at each other's throats. Sister Octavia is a priest from the Cathedral of Light who has been helping the people of Kyovashad by fighting off the evil that has flooded Sanctuary, but, even with great knowledge and exorcism skills, Sister Octavia needs help.
Sister Octavia has a three-part questline that is very rewarding for you to complete. There's not only gold and XP to be had, but Herb and Elixr Caches, Region Renown, and a piece of rare Focus equipment as well.
Malady Of The Soul Quest
You must reach level 20 before unlocking the Malady of the Soul Quest in Kyovashad.
To pick up the Malady of the Soul Quest, you must talk to Sister Octavia in the residential area northwest of the Purveyor of Curiosities vendor in Kyovashad.
Octavia will reveal that a demon has possessed Petr's son, and she needs your help to exorcise the demon. Sister Octavia is a maverick in her own right, as although priests of the Cathedral of Light burn victims of demon possession, Octavia would rather save the victim than give them an agonizing death.
Entering The Frigid Cellar
In the main room of the Frigid Cellar, you will see Petr's son lying on a bed. Octavia will give you her Holy Chalice and ask you to place it by the bed while she references her Prayer Book.
Placing the Holy Chalice on the ground will start the exorcism, and Octavia will begin reading a prayer.
The child will begin to levitate, and Xul'goth will become agitated, summoning several weak Carver mobs to attack you. The exorcism won't continue until you kill all these mobs.
How To Exorcise Xul'goth From Petr's Child
Xul'goth will be summoned once you kill all the mobs in the cellar. Xul'goth, the Chilled Touch, is an elite enemy that has the Summoner and Cold Enchanted affixes, allowing it to freeze you on contact and summon mobs during a fight.
Xul'goth can easily be killed, but you will want to watch out for his heavy attack as it deals major damage. Although it's a slow attack, you won't be able to evade it if you're frozen.
Collecting Your Reward
Once you defeat Xul'goth, Petr's child will be free of the demon, and you'll be able to see Sister Octavia for your reward outside the cellar.
You can use herbs from the Herb Cache to upgrade your potions in Kyovashad.
Depths Of Despair Quest
You will need to leave Kyovashad for the Depths of Despair quest to become available, so either fast travel or go complete a quest and return to Kyovashad.
This time, Sister Octavia needs your help to track down Kvera's husband, Vasek.
The Depths of Despair can be picked up in the residential area northeast of the Purveyor of Curiosities vendor.
Upon arriving at Kvera's home, she will explain that she suspects her husband to be possessed by a demon due to his unusual behavior and outings. Kvera tied up Vasek in the cellar before getting Sister Octavia's help.
Enter the Ominous Cellar and kill the mobs that spawn in the entrance. Once all mobs are dead, you will hear Kvera scream above.
Leave the cellar with Octavia to reveal that Vasek has escaped. Chase after Vasek and follow the trail of blood leading you to the Kyovashad Sewers.
Fight Your Way Through The Sewer
You must fight your way through hundreds of Carvers, Carver Overseers, and Stinging Swarms until you reach the Wastewater Basin. The tunnels have many paths but most link to the end of the sewers.
Once you reach the Wastewater Basin, talk to Sister Octavia to plan your next move. Octavia will give you the Holy Chalice to place next to Vasek, allowing her to start the exorcism.
How To Exorcise Demotath From Vasek
Unfortunately, this exorcism doesn't go as smoothly as the last, and Vasek is killed during the process. You will have to kill Demotath, the Baron of the Frozen Wastes, an elite enemy with the Chilling Wind, Frozen, and Summoner affixes, making this demon a step up in difficulty.
Projectiles won't work as well when shooting through Demotath's Chilling Wind ability, but it's Demotath's ability to summon three frozen orbs that deal high damage and slow your movement.
The small area also makes it hard to maneuver around these orbs. When Demotath summons the frozen orbs, you will have a brief window to evade the area of effect.
Collecting Your Reward
After you kill Demotath, speak with Sister Octavia outside of the sewers. You can teleport back to Kyovashad to get back to the entrance quicker.
Octavia will reward you with an Elixr Cache, a fine reward as Elixrs grant you a five percent XP boost and enhance your defensive capabilities in combat.
Faith In Blood Quest
Once again, you must leave Kyovashad and return to trigger the Faith in Blood Quest to appear.
To pick up the quest, speak to Petr, found near the Kyovashad Waypoint, who will explain that Sister Octavia needs your help.
Petr will hand you a note from Octavia explaining that the wounds from Demotath have gotten worse, and she believes that Demotath was able to escape death by using her as a host.
Meet Kvera at her home before entering the Ominous Cellar to find out how you can stop Demotath from taking over Sister Octavia.
Enter The Ominous Cellar
After speaking to Kvera, enter the cellar and speak to Sister Octavia, who will reveal that you need to find a new Holy Chalice if you exorcise Demotath from her.
Octavia recommends speaking to Matvey, a Chalice Keeper in Margrave, who will instruct you to procure a new Holy Chalice.
Matvey The Chalice Keeper Of Margrave
You can find Matvey by the pyre in the center of Margrave. You deceive Matvey into thinking you are working for Reverend Mother Prava to get the chalice.
However, Matvey will reveal that, in order to convert a chalice into a Holy Chalice, you must perform a ritual requiring you to fill a Silver Chalice with bandit blood.
How To Fill The Silver Chalice With Bandit Blood
To fill the chalice with bandit blood, travel east to the Western Tunnels and Vale of Fool, as these areas spawn hundreds of bandits to kill.
You could complete the Bound by Blood Quest alongside filling the chalice with bandit blood to save time and earn more XP.
You can pick the quest up by talking to Lacthan, who can be found speaking to the townsfolk just north of the pyre.
Once you have filled the chalice, return to Matvey, who will explain that you need to take a burning piece of wood from the pyre and place it in the chalice as the final part of the ritual.
Return to the Ominous Cellar in Kyovashad to begin the exorcism on Sister Octavia.
How To Exorcise Demotath From Sister Octavia
You begin the exorcism using Sister Octavia's Prayer Book and the Holy Chalice. This will anger Demotath, causing him to summon Carvers to attack you. Carvers are easily killed, but you will want to kill the exploding ice carvers before they reach you.
Kill the Carvers and then resume the exorcism by interacting with the Holy Chalice. This will cause Sister Octavia to freeze and summon Demotath.
Demotath has the same affixes as his previous appearance in the Kyovashad Sewers, so use the same strategy and avoid the frozen orbs.
Collecting Your Reward
Once you've defeated Demotath, meet Sister Octavia outside, where she will give you her prayer book.
Sister Octavia's Prayer Book can only be equipped by the Necromancer and Sorceress classes.