Sophia Keren, originally named Negishi Shouko, endured severe bullying in her past life as a Japanese high school student. Mocked as "Vampire" and "Rihoko" for her appearance, she developed deep resentment and a belief equating beauty with worth. She died alongside classmates in an unexplained explosion, reincarnating as Sophia, the only daughter of the noble Keren family in the Sariella Kingdom.

Reborn as a rare vampire progenitor, Sophia initially cherished her new life for its beauty and status. Her early years included a traumatic bandit attack on her family's carriage; saved by a spider monster later identified as Kumoko, the event was misinterpreted as divine intervention. This incident indirectly fueled political tensions, leading to the "Tragedy of Zatona" battle and the eventual destruction of her home by forces led by the elven patriarch Potimas. Her human parents died during this attack, and Sophia turned the family butler, Merazophis, into a vampire to save him. Left without refuge, she and Merazophis joined Kumoko (now called White) and the Demon Lord Ariel.

Sophia's personality is heavily shaped by past trauma. She reacts with intense hostility to anyone using her former name or referencing her past identity, viewing it as a rejection of her painful history. This extends to jealousy toward Shiraori, whom she recognizes as her beautiful, aloof past classmate, Wakaba Hiiro. This jealousy manifested in her acquisition of the "Ruler of Envy" title and its associated Envy skill, disabling opponents' abilities. Her vampire nature craves challenging battles, though rigorous training under Ariel and White left her overpowered, causing periods of boredom or depression. After Ariel confronted her about ingratitude and internal ugliness, Sophia began striving for self-improvement beyond appearances. Paradoxically, years of harsh treatment from White fostered a masochistic dependency, where she interpreted abuse as attention.

Sophia possesses exceptional combat prowess as a true vampire. She exhibits superhuman physical characteristics, statistics amplification, mid-level regeneration, and enhanced senses. Her capabilities include elemental manipulation (ice, water, darkness, poison), spatial maneuvering for flight, precognition, parallel thought processing, and power nullification via Envy. Defensively, she resists most physical and magical attacks, with skills like Immortal Body enabling survival of lethal injuries once daily and Heaven Scale granting mountain-level durability through temporary scales. Notable techniques are "Vermilion Sea," a corrosive blood-acid mixture, and "Shining Blood Mist," which adds freezing effects. Her stats—including "Small City level+" attack potency and "Subsonic" speed—are augmented by skills like High-Speed Calculation, War God Spirit, and Probability Compensation.

Her relationships are complex. She feels detached from her reincarnated human parents, John and Seras Keren, though acknowledging them as "wonderful people." Merazophis serves as her steadfast guardian and father figure; she once harbored unrequited romantic feelings for him. Sophia maintains a rivalry-turned-respect dynamic with Shiraori, while her loyalty to Ariel and White evolved from forced subservience to a familial bond despite enduring their severe training.

Key development events include antagonistic actions during the prolepsis timeline, such as aiding Hugo's coup in Analeit and confronting Shun's party while serving a mysterious "Master." Later, integrating into Ariel's faction involved participating in battles like the assault on the elf village, where she demonstrated her threat level by canceling magic spells and displaying decapitated heads. Continuous abuse and guidance from White and Ariel gradually tempered her vengeful impulses, though her core desire for validation through strength remains.