Kuro, later formally named Chloe von Einzbern, emerged as a distinct consciousness from Illyasviel von Einzbern's sealed memories and capabilities. These memories contained Illya's original purpose as the vessel for Fuyuki's Holy Grail War system, knowledge implanted in infancy by the Einzbern family. Her parents, Kiritsugu Emiya and Irisviel von Einzbern, abandoned the Grail War to give Illya a normal life, leading Irisviel to seal away these faculties and related memories when Illya was around eight months old. A miscalculation in the sealing process caused the sealed memories to develop independently within Illya. Empowered further by Illya's latent wish-granting abilities leaking through the seal as an incomplete Grail vessel, this consciousness eventually utilized the Archer-class Servant Card to manifest physically. This manifestation occurred when Illya used the Archer Card's Install ability to protect herself and others from a collapsing cavern, resulting in a physically distinct entity bearing Illya's likeness but with tanned skin, white hair, and initially clad in the Archer's outfit. Initially identifying as Illyasviel von Einzbern, she was nicknamed "Kuro" (Black) by Rin Tohsaka to avoid confusion. Kuro harbored profound bitterness stemming from her sealed existence, resenting her parents for the sealing and Illya, whose desire for a "normal life" she interpreted as a rejection of her own existence—the manifestation of Illya's magus heritage and Grail vessel purpose. This bitterness drove her initial goal: to eliminate Illya, believing they could not coexist. She viewed herself as the true original consciousness, finding accusations of being a "clone" infuriating. Her personality contrasted sharply with Illya's; she displayed greater calmness, analytical thinking, manipulative tendencies, and a willingness to act brazenly. However, she shared Illya's core experiences and memories up to her manifestation. Conflicts between Kuro and Illya were frequent and intense. A magical seal created by Rin using Illya's blood forcibly linked their sensations, meaning any physical injury, pain, or discomfort experienced by Illya replicated onto Kuro, rendering Kuro's goal of killing Illya impossible as it would cause her own death. Unable to achieve her initial objective, Kuro shifted tactics, attempting to sabotage Illya's cherished normal life. She appeared at Illya's school, draining students' prana through kissing to sustain her unstable form and causing distress. Confronted, she claimed to be Illya's cousin transferring into school the following week and expressed a desire to try living normally. This led to a temporary arrangement where she attended school as "Kuro," Illya's cousin, under the condition she refrain from harming others. Tensions culminated in a magical duel over Illya's normal life and Kuro's place in it. During this confrontation, Kuro revealed the Archer Card embedded within her body and expressed her existential crisis, questioning what would happen to her if Illya regained her normal life. Her physical form began destabilizing shortly after reaching a tentative understanding. Facing dissolution, Illya urged her to fight for her own life. In this critical moment, Kuro admitted her deepest wish was simply to live—not related to being a magus, seeking revenge, or gaining acceptance. This admission activated her latent power as an incomplete Grail, granting her wish and stabilizing her body. Consequently, she was formally adopted into the Einzbern family by Irisviel and introduced to Shirou Emiya as Illya's cousin, Chloe von Einzbern. As Chloe von Einzbern, she became a more integrated family member and part of Illya's social circle, retaining her mischievous and sometimes provocative nature. She demonstrated a caring and protective side, particularly towards Miyu Edelfelt, and showed deep devotion to her friends, prioritizing them over abstract ideals like saving the world. Her affection for Shirou Emiya remained, and she was more forthright in expressing these feelings compared to Illya. She possessed significant magical power inherited primarily from Illya. Her core abilities stemmed from the Archer-class Servant Card (EMIYA) used to create her body, granting proficiency in Projection Magecraft to trace and replicate weapons, including Noble Phantasms like Kanshou and Bakuya, Caladbolg II, and Hrunting, along with the skills and combat experience of their original wielders. She could also utilize Structural Analysis and short-range teleportation (Marble Phantasm metastasis). Her primary Noble Phantasm was Kakuyoku Sanren (Triple-Linked Crane Wings). She required regular replenishment of prana, achieved through draining others' energy via kissing, a process that weakened recipients. She possessed enhanced physical abilities, analytical combat skills, and basic magecraft. Her class skills included Magic Resistance and Independent Action. In her role as an Archer-class Servant in other contexts, her skillset formalized to include Mind’s Eye (False), Projection Magecraft, and Kiss Demon. Following her adoption and stabilization, Chloe continued in subsequent conflicts. She was transported to a parallel world alongside others, found collaborating with Bazett Fraga McRemitz. There, she participated in battles, such as a confrontation with Illya on a rooftop where she was overpowered partly due to prana depletion and Illya's use of the Saber Class Card. She later joined forces with Illya, Bazett, Tanaka, and Gilgamesh to strategize against the Ainsworth family to rescue Miyu. Her relationships extended beyond her immediate family; she recognized parallels between EMIYA (Archer) and Shirou, felt concern upon encountering versions of Irisviel, and exhibited a mix of wariness and curiosity towards other Servants like Suzuka Gozen and Tamamo Cat. Her character evolved from a being consumed by resentment and a struggle for existence to one finding belonging and purpose within her adopted family, while retaining her core traits of protectiveness, pragmatism, and occasional mischief.