The Aqua Jewels

The Aqua Jewels (sometimes referred to Ocean Gems) are 4 magical jewels that are the Ocean Princess's guardians.

Long ago, the 4 gems protected the princess from harm. However, much of their magical powers were sapped, causing them to become insusceptible to protecting her by herself.

The gems made their first appearance in Ultimate Story the Missing Link, when Misty had a dream about hearing 4 familiar voices. She then called Professor Oak to help her find out about any significance to this while also bringing her friends, the Starfox Team, into this. He was able to find that there were magical readings within the bottom of the ocean similar to the voices that she heard in her dream, so she and the Starfox team went to the ocean to investigate.

A long while after traveling through the ocean, they were able to find the aqua jewels, to which Misty was able to regain memories of them. A little afterwards, the gems infused themselves with each of the 4 members of the Starfox team through their crests, giving them aquatic powers that enable them to swim faster and breathe underwater. From there, the 4 members of the Starfox team became the Ocean Princess's new guardians.