The Prism Compass (プリズムコンパス Purizumu Konpasu) is a compass-like device that allows Michishio Shizuku to transform into Ocean Prism, and, like the Smile Pacts, harnesses the power of the Cure Decor pieces. According to Salty, the Prism Compass is a physical manifestation of the songs of the Märchenland mermaids.
The Compass itself is powered by a special Cure Decor piece, unique to Shizuku, shaped like a seashell between two pair of fins resembling a ribbon. To transform, Shizuku sets said Decor at the center of the Compass, turning the needle towards the north, and calling out "Overwash Overture!"
In addition, other Cure Decor pieces can also be inserted into the Prism Compass to grant Shizuku additional abilities and items. Many of them create something little to Salty, like costumes, accessories and food. Also placing special Cure Decor to it, it creates Ocean Prism's primary weapon, the Mermaid Microd.