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. This is supported by official Kemono Friends merchandise, which includes an iPhone case that romanizes the word as "Cellien".

Biology
Ceruleans come in all shapes and sizes. Although those featured in the game and anime were at least half the size of a Friend (and often much larger), research reports included in the second guidebook confirm that Ceruleans early in their development are much smaller, ranging from the size of large insects to microscopic specimens. The fullest extent to which a Cerulean can grow, if there even is such a limit, is unknown.

Early research reports by human experts in Japari Park described the bodies of Ceruleans as "translucent like hard jelly beans", "rainbow-colored and beautiful" and "possessing a texture which is somehow both rigid and wiggly". Their body temperatures cannot be felt upon touch. The properties of the "eye" of a Cerulean are compared to that of a nucleus, and research notes reveal that destroying it causes the entire body to collapse and vanish. Despite their often round and amorphous, algae-like appearance, they are in reality comprised of an assembly of blocks.

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.

Origins
Although it is understand that they are born from Sandstar coming into contact with inorganic matter, the details of Ceruleans' origins aren't fully understood. They were discovered at approximately the same time as the Friends themselves and much of what is known about them comes from research conducted on specimens captured early in their developmental stages.

Ceruleans were present early in Japari Park's history, but were considered a only minor threat to the staff, Friends and park facilities. Early reports equate them to "vermin", but (correctly) make the assessment that larger specimens, which were at that point rarely seen, could pose a much more significant danger.

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.

Trivia

 * Many of the Ceruleans featured in the original game were both named after and designed based on real-life algae.