Fou

Kyasu Parīgu -- also known as Fou-kun (フォウくん) -- is a character that appears in Fate/Grand Order.

He is an alternate iteration of Primate Murder (霊長の殺人者) -- inhabiting those timelines wherein the Common Sense of Man pulses with life, and the Twenty-Seven Dead Apostle Ancestors do not exist as an organization. He is one of the existences referred to as the Beast IV (ビーストIV).

Background
Cath Palug is a member of a species of organism known as the Breed of Calamity (災害の種), which preside over the principle of "Comparison" (比較)

Originally a Beast of the Planet that became Merlin's familiar, Cath Palug was at some point subsequent to Merlin's sealing driven from the Isle of Avalon. In those worlds where the Common Sense of Man is insufficiently prominent, he came eventually to be known as Primate Murder -- the pet of Altrouge Brunestud.

In the timeline of Fate/Grand Order, he came to reside within the Chaldea Security Organization, journeying across the assorted eras of human history in the company of Ritsuka Fujimaru and Mashu Kyrielight.

Cath Palug describes himself as the Beast of Calamity (災厄の獣) that bears the Characteristic (特徴) of "ever exceeding the strength of an opponent" (相手より強くなる) -- growing unto maturation by the conflict that arises amongst Men, feeding upon their Envies (妬み) and Regrets (悔しさ).

Cath Palug is an entity of the Beast class, holding the title of Beast IV. The Beast of 666 from Fate/Prototype apparently holds the same title, but their relationship is presently unknown.

Appearance
Mash Kyrielight describes the Cath Palug as a squirrel-like creature -- "a cute animal," according to his official profile. However, he states that if he were let to normally mature, he would eventually degenerate into a "unsightly monstrosity."

Personality
Removed of the Civilization of Man, Cath Palug would be nothing more than a harmless animal.

He considers Merlin to be a "loathsome wretch," claiming that the man forced him from comfort of the Tower of Imprisonment (幽閉塔) in Avalon against his will. As such, he frequently attacks Merlin on sight.

Garden of Avalon
While Merlin was imprisoned within the Garden of Avalon, he went through the drafts and sketches he had made in life and started telling Cath Palug the events of the life of King Arthur.

Upon witnessing Arthur's final moments, Merlin releases Cath Palug from the Garden of Avalon, insisting that he seek out "that which is beautiful."

Fate/Grand Order
Cath Palug is found by the Chaldea Security Organization and given the nickname of "Fou-kun" (フォウくん) During his stay with the organization, he is permitted to freely wander their facilities.

Fuyuki: Contaminated City in Flames
Cath Palug is met by the Protagonist alongside Mashu Kyrielight.

E Pluribus Unum: Grand Battle of Legends in North America
Merlin uses Cath Palug as a conduit through which to temporarily reveal himself, so to lend aid to the protagonists in the battle against Cú Chulainn Alter.

Salomon: The Grand Time Temple
In the aftermath of Mashu Kyrielight's sacrifice, Cath Palug locates her soul in the place beyond life -- revealing his true name and his nature as a Beast. He then expends the majority of Mana that he's collected across the centuries of his life to transplant his Force of Providence into Mashu's soul, perfectly resurrecting her. However, the act deprives him of his Sapience (知性) nor Characteristic (特性), leaving him as nothing more than a common animal. In the end, he congratulates Mashu and the people of Chaldea for defeating the Beast IV without violence.

Abilities
Cath Palug is capable of enacting a miracle said to exceed the scope of True Magic -- "the Complete Revocation of Death" (死者の完全な蘇生); or, more specifically, the resurrection of Mashu Kyrielight, made possible only due to the extra-temporal nature of Goetia's Reality Marble -- the context of her death.

So to facilitate the resurrection, Cath Palug consumed the majority of the Magical Energy he had accumulated across the centuries of his lifetime, using it to fuel the transference his Force of Providence (運命力) to Mashu, and overwriting the limitations of her remaining lifespan (3 days). However, as he wasn't yet an adult of his species, he was capable only of granting Mashu a lifespan comparable to that of a normal human, at the cost of his Sapience (知性) and Characteristic (特性).

Development
Taiki is the illustrator for Fou.