Shouto Todoroki exhibits heterochromia, with a dark gray right eye and turquoise left eye. His hair is precisely split, white on the right and crimson red on the left. A prominent burn scar covers the left side of his face, resulting from an incident in his childhood when his mother, Rei Todoroki, poured boiling water on him during a mental breakdown induced by prolonged abuse from his father, Enji Todoroki (Endeavor).

His traumatic upbringing was orchestrated by Endeavor, who sought to create a successor capable of surpassing All Might. Isolated from his siblings—Fuyumi, Natsuo, and Toya—Shouto endured brutal training from age five. Endeavor's abuse extended to Rei, culminating in her hospitalization after the scalding incident. Toya (later revealed as the villain Dabi) harbored intense jealousy towards Shouto for replacing him as Endeavor's favored heir, leading to a near-fatal attack during Shouto's infancy. These experiences fostered deep resentment toward Endeavor and a refusal to use the fire half of his Quirk, associated with his father's cruelty.

Shouto's Quirk, Half-Cold Half-Hot, generates ice from his right side and fire from his left. Initially, he rejected his fire abilities entirely, symbolizing this rebellion by incorporating ice plating into his initial hero costume to cover his left side. His combat style relied excessively on ice, causing vulnerability to frostbite and leaving his left flank undefended, stemming from his desire to become a hero without fulfilling Endeavor's ambitions.

A pivotal shift occurred during the U.A. Sports Festival battle against Izuku Midoriya. Midoriya's insistence that Shouto's power was his own reignited memories of Rei's encouragement that he could define his own path. This confrontation led Shouto to reluctantly use his fire abilities mid-fight, marking the beginning of his acceptance of both halves of his Quirk. Post-festival, he reconciled with Rei, visiting her regularly to mend their relationship.

Subsequent development saw Shouto becoming more socially engaged with classmates, though he retained reserved tendencies and occasional social awkwardness, such as misunderstanding flirtatious advances or using overly blunt language. He interned at Endeavor's agency for practical training, acknowledging his father's professional expertise while maintaining emotional distance, explicitly stating his intent to use Endeavor's resources without forgiving past abuses. During the Provisional Hero License Exam, his difficulty synchronizing ice and fire powers highlighted lingering technical and psychological challenges, though he later improved through training.

The Paranormal Liberation War arc forced a confrontation with Toya, revealed as Dabi. Shouto reacted with shock and rage upon learning Dabi orchestrated attacks that nearly killed their brother Natsuo. After Endeavor's defeat, Shouto recognized parallels between his own past hatred-driven behavior and Dabi's self-destructive pursuit of vengeance. He resolved to stop Toya himself, later offering Endeavor a hesitant but tangible gesture of collaboration, extending his hand to help him stand and vowing to confront their family's legacy together.

Shouto's hero costumes evolved alongside his mindset. His initial ice-covered design symbolized rejection of his fire heritage. Later iterations incorporated temperature-regulating technology, tactical vests, and medical-supply belts, reflecting a focus on functionality over symbolism. Post-war designs featured reinforced bracers for storing thermal energy and a distinctive T-shaped stripe representing his family name.

Eight years after the Final War, Shouto graduated from U.A. and became Japan's No. 2 Pro Hero. His physical appearance changed slightly; his scar faded, his hair grew shorter and bushier, and his stature became taller and leaner. His costume retained core elements but added blue accents and a more prominent ice-blue T-pattern.