Shouto Todoroki is the youngest son of the Todoroki family, born from a Quirk Marriage arranged by his father Enji Todoroki (Endeavor) to create a successor combining fire and ice abilities capable of surpassing All Might. As the sole child inheriting both Endeavor's fire and Rei Himura's ice Quirks, he endured isolation from siblings Toya, Fuyumi, and Natsuo for intense childhood training. Endeavor subjected him to physical abuse, pushing him to exhaustion and illness starting at age five. Rei intervened to protect him, leading Endeavor to strike her while Shouto watched. Rei's mental health deteriorated under Endeavor's abuse, causing her to associate Shouto's left side—resembling Endeavor—with trauma. During a psychological breakdown, she scalded his left eye with boiling water, inflicting a permanent scar. Endeavor hospitalized Rei and intensified Shouto's training, blaming Rei for the incident. This cemented Shouto's hatred for Endeavor and his rebellion: refusing to use his fire Quirk. His childhood held covert moments of warmth, including watching All Might videos with Rei and sharing her favorite yogurt drink during hospital visits. At U.A. High School, Shouto initially displayed a cold, aloof demeanor, rejecting social bonds and relying solely on his ice Quirk in combat. During the U.S.J. incident, he efficiently subdued villains in the Landslide Zone but later realized his actions risked freezing allies like Toru Hagakure. His development accelerated during the U.A. Sports Festival when Izuku Midoriya confronted him about self-limiting his power. Midoriya’s insistence that Shouto’s Quirk belonged to him—not Endeavor—reawakened Rei’s past encouragement: “You are not a prisoner of your bloodline.” This prompted Shouto to unleash his fire in battle, beginning his acceptance of both abilities. Post-festival, he reconciled with Rei through letters and visits, discussing events like his match with Midoriya. He interned at Endeavor’s agency for practical training but maintained emotional distance, stating his intent to “use” Endeavor’s expertise without forgiving him. His provisional license exam failure stemmed from Inasa Yoarashi’s grudge over Shouto’s earlier dismissal, mirroring Endeavor’s disdain, teaching Shouto that his father’s legacy would persistently affect his relationships. During the Paranormal Liberation War, Shouto discovered Toya was alive as the villain Dabi. Learning Dabi caused near-fatal attacks on Natsuo and engineered Starservant’s assault, Shouto confronted him in a tearful rage. He later recognized his former self in Dabi’s hatred and vowed to stop him without perpetuating their family’s cycle of violence. Years later, Shouto graduated U.A. and became Japan’s No. 2 Pro Hero. His scar faded slightly, and his costume retained its core design with minor updates. Shouto’s Quirk, Half-Cold Half-Hot, generates ice from his right side and fire from his left. Early techniques like Flashfreeze Heatwave created massive explosions by combining elements, while Flashfire Fist concentrated heat into precise strikes. Later advancements included Phosphorus, a high-temperature fire tornado, and Great Glacial Aegir, fusing ice and fire to manipulate thermodynamics on a massive scale. Overuse risked frostbite or heatstroke, necessitating temperature-regulating costume upgrades like wrist guards and tactical vests. Personality-wise, Shouto evolved from isolated arrogance to deadpan humor and blunt honesty. He misinterpreted social cues, such as assuming Katsuki Bakugo was his friend after supplementary classes, and trolled Bakugo by repeatedly mentioning their progress gaps. He openly challenged authority figures like the police chief during the Stain incident, calling him a “mutt” for reprimanding unlicensed heroics. His interactions with Endeavor during reconciliation attempts included petty remarks about Endeavor’s scar and loud soba-slurping to underscore unresolved resentment. Despite this, he acknowledged Endeavor’s heroic growth and cooperated professionally while demanding earned forgiveness as a father.