Relics is an action-adventure game where players take the role of a spirit who can possess different characters. The spirit appears at underwater ruins with no explanation why it became a spirit and what it needs to do. In fact, one will only find out about the story of the game when seeing the real ending. The graphic style of the game is compared to the works of H. R. Giger.

Players can possess other bodies after killing their owners, but to get the real ending, they must explore the ruins while avoiding unnecessary combat by running away or ignoring the characters they meet on their way. There is no music in the game apart from the opening and the real ending and, depending on the body possessed, players will acquire different skills and attacks.