To join the Dark Brotherhood in The Elder Scrolls IV: Oblivion, follow these steps:
- Kill an Innocent NPC
You must murder a non-hostile, non-essential NPC. Killing bandits or enemies does not count. Good targets are isolated beggars or lone travelers in out-of- the-way places to avoid guards and quest disruptions. Avoid killing shopkeepers, quest-givers, or essential NPCs (marked with a crown icon), as this can lock you out of items or quests
- Sleep in a Safe Place
After the kill, find a safe bed or bedroll (such as in your house or an inn) and sleep. You will receive a message like "The air grows chill and a shadow approaches..." and then be visited by Lucien Lachance, a Dark Brotherhood Speaker. He will offer you a quest called "A Knife in the Dark" to prove your worth
- Complete the Initiation Quest
Lucien will give you the Blade of Woe and instruct you to kill a target named Rufio , who can be found at the Inn of Ill Omen north of Bravil. Rufio is defenseless and can be killed easily, especially at night when he is asleep in the basement
- Officially Join the Dark Brotherhood
After killing Rufio, sleep again. Lucien will greet you and welcome you to the Dark Brotherhood. Your next step is to travel to Cheydinhal , find an abandoned house near the eastern city gate, pick the lock on the boarded-up door, and enter the basement. At the door to the sanctuary, answer the question "What color is the night?" with "Sanguine, my brother" to gain access to the Dark Brotherhood Sanctuary and become an official member
Once inside, you can take on assassination contracts and interact with other members of the guild. This process is the same in both the original and remastered versions of Oblivion
Summary:
- Kill an innocent NPC (not an enemy or essential character)
- Sleep in a safe place to trigger Lucien's visit
- Accept and complete the quest to kill Rufio at the Inn of Ill Omen
- Sleep again and then enter the Cheydinhal Sanctuary using the secret phrase
- Join the Dark Brotherhood officially and start the questline