Cerulean (セルリアン) are a collective name for lifeforms born from when Sandstar joins with a non-organic substance. They're generally non-sentient creatures seeking only to devour in hopes of collecting more Sandstar.
Appearing as the main obstacle for the characters in both the Kemono Friends game and the Kemono Friends anime, Cerulean were first formed after the First Eruption on Japari Island. The outbreak forced Japari Park to close and have all the island's humans evacuated.
Though the park was eventually cleaned out from the Cerulean threat, the Second Eruption caused a larger outbreak that led the park having become a danger to everyone living on the island once again. The park was closed and the efforts by Mirai to save and reopen the park once again failed.
Biology & Behaviour
They appear in several forms and have no defined shape. Though generally monochromatic, some have several colours to their bodies or sport oil-like rainbow shading. Black Cerulean are a particularily dangerous type of Cerulean that can absorb Sandstar Low from afar to grow in strength and size. Some Cerulean are larger than others and show signs of intelligence beyond the need to devour anything in their path.
Ceruleans can't live without absorbing Sandstar and will eventually die out if they exhaust their bodies without devouring or absorbing more of it. A Cerulean will also be destroyed if fully submerged in water. If a Friend is absorbed by a Cerulean, they start to revert back to pure Sandstar, eventually having everything but their life devoured from them. If the Friend is saved from the Cerulean in time, the Sandstar will return the Friend to its original natural animal form.
A unique exception to the usual nature of Cerulean is the character Cerval, a Cerulean learning how to live as a Friend after having taken the form of a Serval Cat. To date, she only appeared in the Kemono Friends game.
A special type of Cerulean known as the Colossal Cerulean can be formed if a Black Cerulean absorbs enough Sandstar Low to grow to gigantic size. These giant Cerulean creatures are near impossible to destroy without having their body submerged in water, due to their amazing strength.