Consult this map for part 4:

Head upstairs and circling around, you will see a door which you cannot open right now. There is a ladder at the corner, use it to climb down. When you see a prompt message, don't go further down yet, circle around again to use another ladder to climb down. From your point of view, move south (Samanosuke's right) you will see a treasure box.

• Item: Power Jewel

Turn around follow the hallway until you see a door, examine it you'll be prompted to open a latch, open it. Backtrack to the first ladder where it prompted you "Go up" and "Go Down", this time choose "Go Down". Inside the room is a box with another Crest Piece. There is a hanging paper on the left wall where you can cut through it to reveal a file.

• Key Item: L. Crest Piece
• File: Journal #4

Now climb back all the way up and use the 2 crests to open the locked door. Enjoy another cutscene. After it finished, turn around and a walk to the next screen. Here you will see a blue book on the right and a wooden box on the left side, they are Seiryu and a hidden Fluorite.

• Item: Fluorite
• File: Seiryu

Proceed to the next room, you will immediately notice a red book on the floor so pick it up.

• File: Suzaku

Before you walk to the next camera view, there is a Three-Eyes waiting to rush into you. So, you either have to walk close to the wall or be ready to block his attack. There is a treasure next to the staircase where you can barely see.

• Equipment: Normal Arrows

Go upstairs you'll hear a boy screaming. Just keep going and kill those Three-Eyes who block your way, then enter the first door you see. There is a treasure box and a blue book, so pick them up.

• Item: Medicine
• File: Seiryu

Walk to the next camera view and cut the 2 screens to reveal a Soul Holder and Magic Mirror, press O to absorb souls. Then pick up another Seiryu.

• File: Seiryu

Use the Magic Mirror to enhance your orbs and weapons and save the game before you go further. Now climb up, watch a cutscene, and enjoy a boss fight.

Boss: Marcellus
The strategy is very simple, Use magic (triangle button), hit, and run. The opening you have is after his attack, you have about 1 second to hit him back.

The boss will drop Arashi (wind orb) after you defeated him.

• Equipment: Shippuu (Arashi)

Go back down, exit the room and continue further until you see a level 1 sealed door with green crystal, open it with Shippuu. Enjoy a very long cutscene which you cannot skip. You might notice a treasure box inside the room during the cutscene. Unfortunately, you will be inside a room in the Keep that is far away from the treasure box after the cutscene is finished. Well, I guess you have to go all the back to pick it up. Remember the door which you unlatched when you climb down a ladder? You can go through that door because it's faster. If you still have trouble, use map below and follow the red arrows.

• Item: Burst Bullets

Now go all the way back to the main hall (where you help the 2 soldiers using bow and arrows). This time, you'll need to help another soldier. He drops Herb.

• Item: Herb

Save your game in the Sentry Room if needed and replenish your magic (where the moth man stays).