Depths of Despair is a side quest in Diablo 4 (Diablo IV). It is located in the Fractured Peaks. You will receive the quest from Sister Octavia at Kyovashad. As a reward for completing this quest you will receive the Elixir Cache. You can un lock the Depths of Despair Quest by completing the Malady of the Soul side quest. Follow the basic steps below to complete this quest.
Basic Steps to Complete the Depths of Despair Quest in Diablo 4 (Diablo IV):
You can start this quest by speaking to Sister Octavia southwest of the Blacksmith. She is in conversation with Kvera about her husband’s demonic possession when you speak to her.


There is a lot of danger inside the Ominous Cellar, which is located within Kvera‘s house. You will be able to return to Kvera’s House once you have killed the demons in the Ominous Cellar.

Once you have exited the building, you will find that Kvera has been injured by her husband. She will ask you to search the town for him.
Taking the blood trail as a guide, enter the Kyovashad Sewers dungeon.

This is the deepest dungeon in the game. In order to reach Vasek, you will have to fight your way through the Kyovashad Sewers, which is the deepest dungeon in the game.
As soon as you reach Vasek, you should perform the ritual for exorcism on him as quickly as possible.
It is during Vasek‘s exorcism that Demotath emerges from him. Defeat Demotath.

After you exit the dungeon, you will be able to complete this quest by speaking with Sister Octavia.