TV-Series
Description
Assassin of Black is the Servant of the Black faction in the Great Holy Grail War, though her loyalty to the faction is nominal at best. Her true name is Jack the Ripper, the infamous serial killer of 1888 London. However, the identity of the real Jack the Ripper has never been confirmed, and this ambiguity shapes the Servant's very existence. The Assassin summoned in this war is not a single historical person but a gathering of怨念, a collective of the怨灵 of countless children who were aborted or abandoned by prostitutes in the Whitechapel district of London and never had the chance to live. These怨灵, born from the victims of society rather than a single perpetrator, manifested as the legendary killer. Their core, desperate wish is not for treasure or glory but to return to the warmth and safety of a mother's womb.

In terms of personality, Assassin of Black is a profound contradiction. She appears as a young girl, pale and dressed in tattered, revealing clothing, and often speaks in a childlike, innocent manner. Her first-person pronoun is "we," reflecting her nature as a composite being of many spirits. This innocent exterior, however, houses a heart that is utterly devoid of understanding for human morality. She kills without malice but also without hesitation, viewing the act as necessary for survival or as a simple fact of existence. Her primary motivation is the search for maternal love. She refers to her Master, Reika Rikudou, exclusively as "Mommy" and shows her a pure, child-like affection. This love is contrasted with a chilling cruelty toward everyone else, whom she will dissect without remorse to feed her need for magical energy or to protect her "mother." She does not see herself as the legendary murderer, as her memories are a fog of collective anguish, but rather acts on the primal instinct to return to the sanctuary from which she was denied entry.

Within the narrative of the Great Holy Grail War, Assassin of Black's role is that of a wild card. Originally summoned by a Yggdmillennia magus named相良豹马, she almost immediately rejected him. When her summoner tried to use her as a tool, she turned on him, severing his hand with the Command Spells and transferring them to六导玲霞, a woman he had planned to sacrifice. This act establishes her key relationship, which is entirely with Reika. Unlike other Masters, Reika is not a magus and cannot provide magical energy through a conventional contract. Instead, Assassin must sustain herself by devouring the souls of humans, a task she and Reika perform together. Their bond is symbiotic and deeply emotional, a twisted family unit within the chaos of war. She holds no allegiance to the Black Faction's goals and interacts with other Servants only as obstacles or sources of food, fighting briefly against Saber of Red and others before being forced to retreat.

The Assassin's development is tied entirely to her relationship with Reika. While she begins as an incomprehensible monster, through her "mommy" she experiences a form of connection and protection she never had. In turn, Reika, a woman who found no value in life, discovers a reason to live and fight for her "daughter." Their journey culminates in tragedy. During a desperate battle, Reika is fatally shot by Archer of Red while shielding Assassin. With her dying breath, she uses her remaining Command Spells not to order, but to beg Assassin to live. This ultimate act of selfless love is the fulfillment of everything Assassin ever desired. After Reika's death, a broken and grieving Assassin is confronted by Ruler, Jeanne d'Arc. Jeanne, understanding the servant's nature as a suffering aggregate of lost children, offers not a sword but salvation. Assassin accepts Jeanne's prayer of purification, allowing her spirit to be cleansed and pass on, ending her existence as a Servant forever.

As a combatant, Assassin of Black is formidable but relies on specific conditions to unleash her full power. Her primary Noble Phantasm is Maria the Ripper, The Holy Mother of Dismemberment. This ability, a crystallization of the Jack the Ripper murders, takes the form of a set of four knives. It is a curse rather than a physical attack, capable of destroying a target's internal organs. Its power increases exponentially when three conditions are met: the target is female, it is night time, and the area is covered in mist. When all three are fulfilled, the target's heart and core are instantly and irrevocably destroyed, bypassing most physical defenses. To facilitate the "mist" condition, she possesses another Noble Phantasm, The Mist, Darkened Misty Metropolis. This is a barrier-type Noble Phantasm that generates a deadly, acidic fog. This mist can kill ordinary humans in minutes, disorients anyone inside, and even reduces the Agility parameter of other Servants. Her personal skills further enhance her killing potential. Information Erasure ensures that after a battle, all witnesses and records lose all memory of her abilities and appearance. The Murderer of the Misty Night skill allows her to guarantee a preemptive strike during nighttime. Despite her childish demeanor, these abilities make her one of the most purely dangerous and unsettling presences in the Holy Grail War, a phantom of fog and knives whose only wish is for a mother's love.