Cetusmon is is a Mega-class Human Hybrid Digimon whose name is derived from the mythological Greek sea monster, Cetus or Ketos. He is one of the Elemental Gods, specifically the God of Water, created by King Royalmon as well as Queen Majestymon, the parents of Prince Signamon. Along with his twin sister, Aquamon, make up the Gemini Twins of Water.
Along with his twin sister Aquamon, they were the first of the Elemental Gods created during the exile of the Royal Family to the Dark Area. It's been said that Royalmon had copied the data of AncientMermaimon, without the latter's knowledge. Unlike the other Elemental Gods, both him and his sister were not only trained by and were bodyguards to Leviamon, one of the Seven Great Demon Lords but also contain part of his data within them. The Mars symbol and the symbol representing the Spirits of Water are imprinted on his clothing. Due to the nature of being born and raised in the Dark Area, Cetusmon's soul has been hardened, with him rarely interacting with the other Elemental Gods or any of the Royal Family, except for Sirenmon. The only form of communication he has with the others is through his twin sister. Due to his connection with Leviamon and the Royal Family, he often scouts the Net Ocean along with Aquamon in order to find hunt down Digimon or recruit them into the Dark Area. While only having contact with Sirenmon, he has the utmost respect for the other members of the Royal Family. His outfit resembles that of the one worn by Aaroniero Arruruerie in Bleach.
- Water Shuriken – Cetusmon forms a shuriken of water in his hand. He then tosses the shuriken at the opponent.
- Water Spout – Cetusmon's body glows light blue, then he fires a blast of water from either his mouth or his hands at the opponent.
- Shell Blade - Cetusmon's one or two hands start to glow yellow. A light blue aura then appears and hardens around them, forming into one or two curved blades of energy. Cetusmon then slashes the opponent with the blades.
- Rain Prayer - Cetusmon's body becomes surrounded in a crimson red aura, making a storm appear. Or Cetusmon's body glows white and releases steam from his body, causing a large raincloud to appear above the battlefield.
- Black Mist - Cetusmon takes a deep breath and releases a thick black or dark purple smoke from his mouth onto the battlefield. He also uses this attack to cover his escapes or to sneak onto his opponent.
- Bubble Beam - Cetusmon's hands glow white or blue and then he shoots blue or white bubbles from his hands at the opponent. Or Cetusmon opens either of his hands and releases light blue, orange multicolored, or blue bubbles at the opponent from both or one hands.