The Eye of Truth is an Out of Place Artifact in Star Ocean: Fantastic Space Odyssey and its remake Star Ocean: First Departure. It is located on the world of Roak, and is the subject of many legends, such as it having the ability to grant one all of his or her wishes, or to be able to see anything they wished, no matter where it is.
The Eye of Truth was built by the Muah stranded on Roak millenia ago. They built it using their technological knowledge and the symbological powers of the Roaking natives, the Runes. The Muah had intended to use it to open a portal back to Earth, but instead opened a portal to the Demon World. After closing the portal, the Muah decided it was too risky to use the Eye and locked it away. They also left clues on how to obtain the relic in case of need to the four royal houses of Roak, and an Emblem to each. This way, the Eye of Truth would only be obtained with the cooperation of the four kingdoms of Roak.
When the party visits the Purgatorium, they are greeted by three somewhat rude AI powerd holograms that act as the interface of the Eye, named Runes. During this vist, the legend that the Eye can locate any person alive or dead is proven false, as they are unable to detect Ioshua's sister. They are, however, able to detect lifeforms that are from different periods of time by sensing their temporal axis. This allows them to locate Ronyx and Millie. They also possess the ability to transport others, as they teleport Roddick and company out of thier cave.
The party later return and travel far into the Inner Purgatorium to retrieve the Eye. Using the Eye, they use it to open a portal to the Demon World to confront Asmodeus.