Appearing as one of Riviera's Battle Items, Silvia is the strongest of the spear type weapons.
Obtaining the 50x Silvia is a convoluted procedure spanning many chapters:
1. Capture the White Butterflies in the Royal Tomb in the Nelde Ruins.
2. Before Chapter 4, talk to Ritz in the Crystal Caverns to release the butterflies.
3. After Chapter 4, examine the Butterfly Spot in the Crystal Caverns to obtain the Diamond Teardrop.
4. Give the Diamond Teardrop and all spears to Chappi.
5. Silvia can be only be collected from Chappi after Chapter 5.