Beast

Beast (ビースト) is a non-standard Servant class populated by the seven entities classified among the Evils of Man (人類悪) -- the common designation for the Beasts of Calamity (災害の獣). It is for the purpose of acting as a fail-safe (安全装置) by which to counteract the Evils of Man that the Seven Servants of the Station of the Crown (七つの冠位クラスのサーヴァント) are summoned forth.

Overview
In more concrete terms, the Evils of Man are, as the name implies, the Stigmata of Humanity (人類の汚点) -- the seven Calamities (災害) positioned to enact the annihilation of Man; that threaten the continuity of the History of Man (人類史) with stagnation. Being entities that obtain standing within the World of the Primates (霊長の世) by way of factors that grow forth from human society and the Common Sense of Man (人理), the Evils of Man are existences that accumulate strength in proportion to the advancement of Man, and are in essence as cancerous cells (癌細胞) that consume Humankind (人類種) from within. Being born of civilization, they are beings that consume civilization -- the embodiment of the destruction visited upon the works of Man.

Rather than Servants brought forth via the evocations of spells founded upon "the Combat Ritual For the Salvation of the World" (世界を救うための決戦術式) -- "the Summoning of the Heroic Spirits" (英霊召喚) -- the Beasts are the original beings that came to hold spiritual stature (霊格) as Saint Graphs (霊基) ; the basis and archetype of the Heroic Spirits, which by the causality of self-inflicted karma come to act as a system for the of Man (人類の機構).

Though the Beasts can be said to represent the Seven Sins of Humanity (人類の七罪), the sins represented are not the seven carried away upon the death of the Savior. Rather, they come of the attributes that humans embody in existing as humans; those things that cannot be set aside so long as one continues to subsist as a creature cursed with Wisdom (知恵). Being encompassing of all humanity, the Evils cannot be withstood or overcome; for just as Humanity is incapable of abandoning Wisdom, so too are the Evils an inevitable fixture of the Human Condition.

However, by the word of Gilgamesh in the 7th Singularity of Fate/Grand Order, the Evils of Man are the Calamities over which Humanity is destined to prevail.

Class Skills
Entities of the Beast class are believed to possess Independent Manifestation (単独顕現) as a common Class Skill -- a capacity comparable to a limited version of the Third Magic, which permits the unrestricted projection and materialization of the soul (魂の物質化) of the skillholder into a time period of his choosing. Being that the skillholder's soul fundamentally exists beyond the boundaries of life and death and the limits of the History of Man, apparent time travel is possible; and the projected flesh is in essence an immortal puppet controlled by the skillholder's consciousness.

Independent Manifestation is otherwise thought to be a skill shared among the Grand Servants.