How to get this quest
Complete Rise to Intermediacy, then enter Trademond.
Beginning
Speak to Sardine, then go to Draknor Fortress. You'll get greeted by Sathanas. Your goal is now to reach floor 5 of the fortress.
Resistance mechanic
When entering the fortress area, Aura gets a Resistance counter. The counter starts at 10 times Aura's MDEF. If Aura's MDEF decreases while inside the fortress area, the counter will decrease accordingly. Raising Aura's MDEF inside the fortress area won't increase the counter. The counter will decrease with each step and turn in battle. Starting a new day will reset the counter.
When the counter reaches 0, Aura gets affected by the Arms of Wrath curse. If you want to avoid this, it is advised the quest progressively and set up rope shortcuts on your way.
From the exterior to floors 1-2
You start on the fortress exterior. There are two entries to the building.
The stairs leading to floor 3 are on floor 2's west wing.
Curse traps and demon incarnations
There are three demons blocking some parts of the fortress.
The incarnations respawn each day as long as their associated core is not defeated.
Besides making progression over multiple days easier, defeating a demon's core gives 1 corruption, 2 max corruption and 50 exp.
Drakhnor Fortress also contains multiple curse traps. Some off them must be walked on to access Aamon's and Kerberos's domain. Furthermore, Moloch's domain is protected by a tentacles group and this fight can be avoided if you walk on a curse trap. There is a way to walk on the traps without suffering their effect.
On floor 1's west wing, there is a group of two adventurers: Matthias and Mira. As long you are in their room, the Resistance counter doesn't decrease. Finally, up to once per day, talking to Mira and asking for her help allows you to give a blessed energy potion+ in exchange of the spell Curse Trap Barrier. This passive skill last until the end of the day or walking on a curse trap. When such a trap triggers, the barrier protects Aura.
From floor 3 to floor 5
The stairs leading to floor 4 are guarded by Jonas, accompanied by Siegfried and two regular enemies. You can avoid this fight altogether by luring the troop and having it follow you around the staircase in the top right of the map . Siegfried is the main damage dealer of the group, and Jonas is a tank able to use Protect II. To win the fight without removing Aura's collar, two approaches are valid:
Floor 4 is pretty small. The path is straightforward, but Moloch's core is a tough boss able to summon multiple tentacles and buff them. Moloch also summons 3 poisoned hungers (fragments with poisonous attacks) mid fight when taking enough damage. Ambushing Moloch with Shadowcloak I and a slime boosted by Bloodshot Eyes drug is an advised strategy to win without removing Aura's collar. Radiance I also makes the fights pretty easy, but the skill takes time to acquire.
Confronting Sathanas
Sathanas can be confronted on floor 5. The encounter is divided into two parts.
Beating Sathanas gives 2 corruption, 5 max corruption and 250 exp and an harvestable spot increasing Aura's max MP by 15. But victory is optional in the quest. Sathanas and his army will leave Drakhnor Fortress even if Aura is defeated. In this case, you get the Arms of Wrath curse (if Aura doesn't have this curse already) and the day ends.
Completing the quest
Examine the castle ruin on the world map. You will obtain the Caritas Rune. After obtaining this item, reporting to the guild clerk becomes possible. You then get the reward and complete the quest.