Instructions
Enter 2-3, or Flamelurker Archstone, and make your way to the Dragon God. Clear the debris on the right and left walkways to reach the ballistae on either side. Use both to incapacitate the Dragon God and then attack his head when he's pinned. After killing Dragon God, collect the Dragon God Soul.
Go to 4-2, or Adjudicator Archstone. Rescue St. Urbain after meeting Patches the Hyena, and he will return to the Nexus. Defeat or otherwise exit this world and return to the Nexus.
Speak to St. Urbain in the Nexus and give him the Dragon God's Soul. He will reward you with the Rage of God, or God's Wrath, miracle, as long as you have at least 16 Faith, which gives you two miracle slots.