Theresa Apocalypse, originally designated A-310, emerged from Otto Apocalypse's 1972 genetic experimentation as a synthetic lifeform. Her unique genetic fusion blends DNA from Kallen Kaslana and the Honkai Beast Vishnu, granting enhanced abilities like superhuman strength, rapid regeneration, and high Honkai resistance. This hybrid composition permanently locked her physical appearance to that of a twelve-year-old girl, marked by white hair in a low side ponytail and bright blue eyes, despite her chronological aging. Created as part of Otto's project to resurrect Kallen, her lineage traces to failed A1/A2 clone batches. The subsequent A3 series incorporated Vishnu's genes, halting aging around twelve. After surviving competitive trials against fellow clones, A-310 spared her final opponent, A-303. Otto, recognizing her distinct individuality beyond Kallen's shadow, renamed her Theresa and adopted her as his granddaughter. Her personality echoes Kallen's kindness and protectiveness, tempered by stubbornness and tactical use of her childlike appearance. Though mature in leadership roles, she indulges in sweets, HOMU merchandise, and covert manga reading. Combat dialogue often features boasts about her "cuteness" or playful enemy taunts. As an S-rank Schicksal Valkyrie, she clashed with the Herrscher Sirin during the 2000 Second Eruption. Sirin tried recruiting her over shared Schicksal mistreatment, but their duel left Theresa impaled by a void lance—later rescued by Welt Yang and Siegfried Kaslana. Otto then revealed the Oath of Judah's latent "0th Power," nullifying Honkai energy at lethal risk to herself. Theresa activated it against Sirin, stabbing her heart. Believing Sirin dead, she deactivated the power, enabling Sirin's Gem of Serenity-fueled regeneration. Otto altered Theresa's memories to fit Schicksal's narrative. She bonded deeply with Cecilia Schariac, self-styling as "aunt" to Cecilia's daughter Kiana Kaslana. After Cecilia's death in the Second Eruption, Theresa conspired with Siegfried to save Kiana from Otto. Siegfried escaped with clone K423, while Otto kept the original Kiana. Trapped by Otto's leverage over Kiana, Theresa transferred to Schicksal's Far East Branch. There, she founded St. Freya High School on June 21, 2009, serving as principal. Post-Nagazora incident in 2014, she recruited amnesiac K423 (believed to be the real Kiana) into St. Freya. Learning K423's clone origin during the Anti-Entropy Invasion, Theresa still shielded her, culminating in open rebellion against Otto at the Battle of Schicksal. In *Cooking With Valkyries*, Theresa appears directly in chapters 3, 5, 6, 7, 8, 9, and 12, with a cameo in chapter 10, engaging in slice-of-life meal preparations with other valkyries. Additional traits include a fear of ghosts, preference for bitter melon juice, and using "TERITERI" as the Hyperion's security password.