Sofia Sakharov, a Russian seventh-grader at Aibo Academy, balances her role as middle school student council vice president with a covert identity as Disaster’s undercover agent. Bound by unwavering loyalty to the group’s leader, Kyoya Gaen, she executes missions with cold precision, her demeanor marked by calculated calm and fleeting glimpses of malice or irritation. In Season 1, she orchestrates schemes like distributing Dark Core Deck Cases and manipulating the Gaen Cup, leveraging psychological warfare and strategic card combos like "Great Fate, Frozen Stars" paired with "Astraeus" to dominate opponents. Her flawless record shatters only when Tetsuya Kurodake exploits her vulnerability to provocation, prompting her to erase evidence via self-destruct protocols after Kyoya’s defeat.

Adopting the alias Death Shido in Season 2, Sofia allies with Ikazuchi to hunt the Fifth Omni Dragon Lord, Tenbu, while deploying shields to deflect punishment onto her subordinate Shido. Shifting deck strategies from Danger World to Star Dragon World, she prioritizes rapid gauge accumulation and Crossnization tactics. Her infiltration of the Buddyfight Club collapses after Suzaku Kenran exposes her, yet her allegiance remains ambiguously tied to both Ikazuchi and Kyoya—until later events confirm her continued loyalty to Kyoya’s shadow agenda. She inadvertently fuels a dystopian timeline by aiding Tasuku Ryuenji’s time travel, then escalates her influence by awakening the Eighth Omni Lord and wielding Inverse Variable Cord during the Omni Lords’ conflict.

Corrupted by Yamigedo’s spirit, Sofia suffers petrification after a duel with Tasuku, only to resurrect through Disaster Force and resume furthering Kyoya’s ambitions. Her final act—teleporting Kyoya to safety during Yamigedo’s downfall—cements her legacy as a resilient enabler of Disaster’s goals, her ultimate fate lingering in uncertainty. Across both seasons, her mastery of Disaster Force grants abilities like teleportation, incapacitating foes, and shifting her appearance to feature serpentine eyes and elongated hair, while her evolving deck strategies mirror her adaptability in advancing Kyoya’s schemes.