Joan of Arc is at the top of Prison Tower. Follow the Warrior clue and climb to her rooftop encounter in Castlevania: Belmont's Curse, then use your dodge's invincibility frames against her flaming sword swipes, backstabs, and fireballs. Defeating her gives you another key and the Warrior card, with Holy Light opening a way through Chaos Shards.
Where is Joan of Arc in Prison Tower?
Climb Prison Tower to the top to find Joan of Arc, the guardian identified by the Warrior clue. The clue banner reads “The Warrior is at the top of the Tower,” and the spirit explains that she was trapped there before the flames took them.

- At the cemetery and tower junction, follow the sign toward Prison Tower, to the right. The left arrow points toward Holy Innocents' Cemetery, the cemetery destination also referred to as Innocence Cemetery. Keep climbing for Joan; the cemetery is the other way.

- As you climb, follow the clue to find cranes inside or outside the tower. Near the spirit, Rose notices a crane and a scrap of parchment. Look for the spirit in the narrow alcove surrounded by spikes, and check your area map when you need to orient yourself.

- Continue to the top. During the rooftop conversation, Rose identifies Joan of Arc and asks for her key to the catacombs.

How do you beat Joan of Arc in Prison Tower?
Learn Joan's attack patterns and dodge her flaming sword swipes, backstabs, and fireballs using your dodge's invincibility frames. Don't rush her: she punishes greedy attacks. For more on the encounter, head to the Joan of Arc boss section.
Prepare your health before committing to the rooftop fight. One player reached Joan without healing to spare, lost the attempt, and had to climb back from a spawn point farther down the tower. Once the encounter began, they could no longer back out.

Healing and spells both spend mana, which you recover by defeating enemies. Keep some for healing rather than spending it all on spells before the fight. With PlayStation controls, Circle handles dodge and slide, a double tap lets you flip backward, and L1 heals.
What do you get after beating Joan of Arc?
You receive another key, and Joan appears on the Warrior card in Rose's tarot deck.

Joan's Arcana gives you Holy Light. Her Burnt Sword of Fierbois also has a charge attack; see the weapon types if you want to explore your combat options. The tarot cards page covers the deck that holds your defeated guardians.
How do you use Holy Light to pass Chaos Shards?
Hold L2 to use Joan's Holy Light and traverse through Chaos Shards. At the blocked route, The Fallen identifies the shards as matter from the Abyss and tells you that only holy light can penetrate them. Switch to Holy Light here instead of trying to break the obstruction with a weapon.

Holy Light can also deflect enemy attacks when you time the press perfectly.
Next, head to the cemetery and the ruins beneath it, where Medusa holds the last key: Cemetery and Underground Ruins.