Feres, also known as Ceres, Selece, or Seresu, functions as Umi Ryuuzaki's Rune God (Mashin) in Cephiro. Created by the world's architect, Mokona, it stands as one of three legendary guardians, embodying the water element alongside benevolence and the present moment. Its name originates from the Toyota Corolla Ceres automobile.

Typically, this guardian manifests as a large blue European-style dragon. However, its appearance shifts in the OVA adaptation, taking on the form of an Eastern-style serpentine dragon with smaller limbs and no wings. Feres resides within an undersea shrine accessible only to its chosen candidates. Summoning requires locating the Sea Temple in Cephiro's ocean, where its image is carved, and passing a trial of inner strength.

Umi Ryuuzaki awakens Feres during the Magic Knights' quest to save Princess Emeraude. As Umi's partner, it confronts adversaries like Zagato and later, Princess Emeraude's vengeful incarnation. Mirroring Umi's fencing prowess, Feres prioritizes speed and agility in combat. It amplifies Umi's water-based magic, enabling spells such as Water Dragon and Azure Hurricane, and possesses the unique ability to project destructive light from its fists.

Within the divergent 1997 OVA storyline, Feres contacts Umi during an invasion of Tokyo by Cephiro's forces, proposing a pact to battle the sorcerer Ascot. Emerging from the sea in its serpentine form, it bonds with Umi mid-battle, transforming into its combat-ready state for the conflict.

Across all depictions, Feres remains a steadfast ally to Umi, consistently symbolizing water's attributes of adaptability and flow. Following the dissolution of Cephiro's Pillar system, it departs alongside Mokona and the other Rune Gods to traverse dimensions, ending its direct involvement in the world's affairs.