Sofia Sakharov, alias Death Sophia, begins as a secondary antagonist in the series' first season, shifting to a tertiary role in the second. This female Russian character is a seventh-grade student at Aibo Academy. She operates undercover within the middle school student council while secretly serving the Disaster organization. She maintains a calm and serious demeanor, rarely expressing emotions beyond malice or annoyance. Highly intelligent and responsible, she commits fully to her roles, whether as student council vice president or a Disaster operative. Her loyalty to Kyoya Gaen is absolute, leading her to follow his orders without question or hesitation. This loyalty later extends to Ikazuchi in Season 2, though she prioritizes self-preservation, using shields to avoid punishments meant for collaborators like Shido. Her composure can shatter under provocation, resulting in outbursts—a noted weakness by Kyoya. She can feign cheerfulness when necessary, though it causes her physical discomfort. During Season 1, she acts as Shido's assistant within the student council while covertly recruiting fighters for Dark Core experiments. She targets individuals like Genma Todoroki and Jin Magatsu as potential replacements after Rouga Aragami's departure. She participates in the ABC Cup and later aids during the Gaen Cup as part of Team Purgatory, securing an easy victory against Shusui Kanahebi. Her confidence and pride show during her match against Tetsuya Kurodake, but she loses when Asmodai breaks her focus and Tetsuya rallies. Later, under Kyoya's orders, she attempts to erase Rouga's memories, an effort that is halted. During the final match between Tasuku Ryuenji and Gao Mikado, she tries to enforce a false ruling against Gao using Berserk Gard but is thwarted and injured. She helps Kyoya defend the portal generator, clashes with Kiri Hyoryu and Rouga, and triggers the generator's self-destruct before escaping with Elf Kabala. In Season 2, she collaborates with Shido under Ikazuchi's command to capture the Fifth Omni Dragon Lord, Tenbu, using the Hundred Demons. She creates and adopts the "Death Shido" identity for undercover work. She impersonates Death Shido to divert suspicion from Magoroku, fights Suzaku Kenran while investigating the Buddyfight Club, and loses after Kenran reveals her true identity. Her loyalty to Kyoya resurfaces when she assists Tasuku in traveling to the future to retrieve Jackknife Dragon, aligning with Kyoya's investigation into Star Dragon World. In this future timeline, she encounters children resembling her and Tasuku. Later, she demonstrates loyalty to Gratos by using her Disaster Force to awaken the Eighth Omni Lord at Cho-Nagoya, an act that drains her energy. She participates in sealing the Omni Lords on the moon and gains control of Inverse Variable Cord after Yamigedo's revival. Positioned as a barrier beneath Aibo Academy to obstruct the Omni Lords, she initially intends to allow Tasuku passage per Kyoya's instructions but becomes corrupted by Yamigedo's spirit. While possessed, she fights Tasuku, loses, and turns to stone. Variable Cord later un-petrifies her using Disaster Force and a Dark Core, explaining the ability reverses petrification. She unseals the Inverse Omni Lords from defeated fighters and delivers them to Kyoya for his attempt to control Yamigedo. She later uses her Disaster Force alongside the Photon Saber, Meteor to combat the Hundred Demons. Her abilities include activating Disaster Force, which alters her hairstyle and narrows her eyes vertically. This power enables teleportation, renders people unconscious, and manifests card effects into reality. She also possesses impersonation skills, evidenced by her convincing portrayal of Death Shido. A specific spell card named "Buddyfight Triple T 'Sophia Sakharov'" exists in the Legend World attribute, functioning as a protective counter for Star cards. She survives multiple confrontations, including petrification and energy depletion, ultimately continuing her service to Kyoya Gaen's objectives.