Poseidon  

, ポセイ・どん

One of the characters resembling the monster from the creature from the black lagoon, who belongs to the mermaid race, is much larger than humans and other merfolk. his size can be compared to hills and buildings. in the manga, he lost a duel against riza and died afterward. however, in the anime, he survived the battle and fell in love with riza. although he did not have a name in the manga, he was later given the name poseidon in the anime.