This Elden Ring questline involves D, Hunter of the Dead, and his mysterious twin brother. Completing it rewards you with unique items and lore insights.

Steps:

1. Meet D at Roundtable Hold:

* D can be found near the fireplace in the Roundtable HoldLandmark early in the game.

* Exhaust his dialogue to learn about his search for his missing twin brother.

2. Find D's Twin Brother's Note:

* Travel to the Fortified Manor in LimgraveRegion, west of the Agheel Lake.

* Defeat the Cleanrot Knight guarding the entrance.

* Inside the manor, climb the ladder to the upper level.

* Find a corpse on the balcony holding a note titled "D's Brother's Note."

* The note mentions the Black Knife Assassins and their connection to D's brother.

3. Defeat the Black Knife Assassin at Roundtable Hold:

* Return to the Roundtable HoldLandmark and rest at Grace.

* A Black Knife Assassin will invade your world while resting.

* Defeat the assassin to obtain the Black Knife Set, Black Knife, and Black Knife Tiche Ashes.

4. Talk to D about his Brother's Death:

* Speak to D again after defeating the assassin.

* He mourns his brother and reveals he was also a Black Knife Assassin.

* Give him D's Bell Bearing obtained from the assassin for the Twinned Set.

5. Exhaust D's Dialogue after giving the Bell Bearing:

* Talk to D repeatedly until he has nothing new to say.

* He might offer the Black Knife Parry as a reward.

Optional:

* Complete Black Knife Assassin Invasions:

* After defeating the first Black Knife Assassin, more assassins might invade your world throughout the game, especially in areas connected to the Black Knives (e.g., Black Knife CatacombsGrace).

* Defeating them might grant Black Knife Tiche Ashes (optional).

Rewards:

• Black Knife Set
• Black Knife
• Black Knife Tiche Ashes
• Twinned Set (from D's Bell Bearing)
• Black Knife Parry (optional)

Lore Implications:

• This questline reveals the Black Knives' role in the game's lore and their connection to the demigods.
• It sheds light on D's past and his conflicted feelings towards his brother.