Yoko Belnades, located in the castle's shop area, offers Item Synthesis. This allows you to combine certain souls with weapons to create more powerful versions or entirely new weapons. This is crucial for obtaining some of the best equipment in the game.

How it Works:
- Talk to Yoko: Select the 'Synthesize' option.
- Choose a Base Weapon: Select a weapon from your inventory that can be synthesized.
- Select a Soul: Choose the required soul for the synthesis. Each synthesis recipe requires a specific soul.
- Confirm: If you have the necessary weapon and soul, you can proceed with the synthesis. The original weapon and soul will be consumed, and a new, stronger weapon will be created.
Many powerful weapons, such as the Claimh Solais (requires a Claymore and a Buer Soul), are only obtainable through synthesis. Keep an eye on your inventory and the souls you collect, as you might unknowingly have the components for a significant upgrade. Some synthesis recipes are hidden, requiring experimentation or consulting a guide.