Ludwig, the Holy Blade (Head) — Bloodborne

Quest overview

Collect the Holy Moonlight Sword immediately before advancing Simon's quest.

• Defeat Ludwig.
• For the peaceful handover, wear chest attire recognised by the Church.

• Do not advance Simon beyond the arena before collecting the sword.
• Do not use the Choir Bell to heal the head: the wiki reports that it can kill it.

Find the head near the exit

Underground Corpse Pile · left of the exit stairs

Immediately after Ludwig

• Approach the head left on the ground.
• For the peaceful option, equip Black Church, White Church, Choir, Executioner, Tomb Prospector or Gascoigne chest attire before speaking.

The dialogue offers a yes/no answer if your attire is recognised.

Direct route: answer yes

Same arena

With Church chest attire equipped

• Answer yes to Ludwig's question.

Holy Moonlight Sword obtained immediately.

Other routes if the sword was not handed over

Same arena

Before continuing Simon's quest

• Without recognised attire, you must defeat the head to collect the sword.
• After answering no while wearing Church attire, reload: Simon may come and finish Ludwig off. Speak to him then to receive the weapon.

Check that the Holy Moonlight Sword is in your inventory before leaving.

Letting Simon progress further without collecting the weapon may make it missable, according to the wiki.