Cellien

The Cerulean (Japanese: セルリアン Hepburn: Serurian) are an aggressive, invasive species of monster which is formed by the union of Sandstar and inorganic matter. They are mainly amorphous in shape, although they come in various shapes, sizes and power levels. They are the collective antagonist of the Kemono Friends multimedia franchise. Ceruleans are a threat to Friends and humanity alike, absorbing and devouring them if given the opportunity.

Etymology
The origin of the name "Cerulean" is not known for sure. While it's tempting to assume it refers purely to the shade of blue or cyan, Ceruleans across all Kemono Friends media in which they are featured come in many different colors. One prevailing theory on the word is that it is a portmanteau of cell and alien, owing to their typically amorphous, cell-like appearance and otherworldly, invasive character.

Biology
Ceruleans come in all shapes and sizes, but tend to be at least as half as large as a Friend. All Ceruleans featured in the anime have been groundbound, however species capable of levitation and flight appeared in the original game. A great range of strength between species can be observed in all Kemono Friends media in which they appear; there are weak Ceruleans as well as very formidable ones possessing advanced capabilities. It is revealed in the anime that they feed off of Sandstar, explaining their tendency to hunt Friends.

In the original mobile game, Ceruleans explode into block-like fragments after receiving sufficient damage, and a triumphant "パカァーン！" (Pakaan!) is displayed on the screen. In the anime, a Cerulean is usually defeated by striking an exposed stone somewhere on its body, at which point it bursts into blocks as usual.

The Ceruleans' origins are largely a mystery. It is understood that they are the product of Sandstar coming into contact with inorganic matter, however details about their initial discovery are unknown. It appears that they came to exist some time after Friends did.

Behavior
Unlike Friends, whose behavior largely resembles that of humans despite their animalian heritage, Ceruleans are almost exclusively depicted as mindless and aggressive monsters. They are a major threat to other organisms, and their presence has been the cause of at least two evacuations of Japari Park. Ceruleans feed off of Sandstar as well as organisms formed by it, which is why they mercilessly attack Friends, but they are evidently a threat to humans as well. Upon locating a target, they will attack it mercilessly, a process which only ends with the prey escaping or through the death of the Cerulean itself. Friends that are devoured will lose their human form and revert to their original, animalian body thereafter. They survive the process with their lives, but at the expense of all their human-like capabilities, as well as the memories gained as a Friend.

In the original Kemono Friends game, they are responsible for stealing Sparkle from Friends and humans alike, and can use it to transform into more advanced forms. Cerval and the Cerulean Queen are two such examples.

Variants
There are a great many types of Ceruleans encountered across Kemono Friends media. Many of them are fairly generic and have no special properties beyond their combat strength, however a few unique examples exist and warrant direct mention.

Cerval
A Cerulean resembling Serval with several irregular properties, who is in possession of Serval's unique Sparkle. Unlike regular members of her species, she is capable of speech and emotion, developing a friendship with her Friend counterpart over the course of the original game's story. At the end of the game, she joins the player party as a full-fledged Friend.

Cerulean Queen
Also appearing in the game, the Cerulean Queen once possessed the sparkle of Kako, enabling it to grow incredibly powerful. It is the antagonist of the game's plot, and was defeated by the player's party at the story's conclusion. Upon defeat, it reverted into its true form: an unremarkable, basic Cerulean, which immediately scurried away.