Vault Keys are essential for unlocking the Chaos Emerald vaults on each island. These are primarily earned by achieving high ranks (A or S) in Cyber Space levels. Each island has a set number of Chaos Emeralds, and each requires a certain number of Vault Keys to open its vault. Collecting all Chaos Emeralds on an island is often a prerequisite for facing its respective Titan Guardian and progressing the main story. Aim for those S-ranks!
