Sea Demon, also knows as the Dark Ones, are enormous blue sea creatures. They are territorial but not predators. When preparing to attack, the sea demon’s body begins to heat up and glow a burning red. Water boils around them when they grow hot in attack. They swim extremely fast, large, and very aggressive to trespassers. They hate the black whales, which are said to be myths or blocked behind the Evergates, but have been sighted a few times during the series.
Sea Demons are naturally docile and intelligent creatures, and there were once many of them living within the Cerulean Sea. The only Sea Demons alive during the events of the series are far more aggressive, and are eventually revealed to be inhabited by the wills of previous Prisms, including Lucidonius and his wife, the second Prism. These Prisms had decided they would rather live on in the body of a the large beasts than be killed after finishing their tenures as Prism.
They attack and eat Banes while they form, keeping the colors in balance.
The only known man to have killed a Sea Demon is the crazed pirate Gunner, who shot one of them down using a cannon. Nine were known to exist until Gunner killed one, in doing so he unbalanced the harmony in color magic.