The U.A. Sports Festival in My Hero Academia is still one of the best pieces of character work in the series. The first match of the second round highlights Izuku Midoriya's devotion to being a hero while expanding upon the backstory of Shoto Todoroki, arguably the series' most compelling character. As Shoto refuses to use his full power out of hatred for his father, Midoriya, aka Deku, does everything he can to help his classmate see the error of his ways, even if it costs him the match.
Shoto Todoroki has had a hard life as the son of Endeavor, the Number Two Hero. Endeavor's obsession with surpassing All Might made him abuse his own son to turn him into a strong enough hero to usurp All Might as Number One because Endeavor knew he could never do it himself. Shoto's Quirk is Half-Cold, Half-Hot, yet he refuses to use the fiery half of his Quirk because of Endeavor's own flaming Quirk. The young Todoroki intends to fully reject his father by winning the Sports Festival without ever using his flaming right half.
When Deku's and Shoto's match begins, the One for All successor immediately resents that, unlike everyone else, Todoroki is not giving his all in this competition. Deku points out that, despite the immense power of Shoto's ice, he has not actually damaged Midoriya in their fight, as Deku's wounds are his own doing. Midoriya also notices that after many attacks, Shoto's body has patches of ice on it, and he is trembling. Deducing that there is a limit to how much ice Shoto's body can withstand, Deku points out that it's a problem that Shoto could easily overcome by using his flames.
Deku demands that Shoto fight using his full power because he will never achieve his dreams if he is only using half of his strength. In the stands, both All Might and Endeavor realize that Deku is trying to help Shoto, even though it's in his best interest to allow Todoroki to keep fighting with one arm tied behind his back. When Shoto reacts angrily, Deku further demonstrates his point by landing a solid blow despite being heavily wounded, because Shoto's body is too cold and stiff to move quickly.
Deku shows that he better understands what it means to be a hero with his ability to give his all even if it destroys his own body. Meanwhile, Todoroki refuses to give it his all because of his own anger and insecurity. When Shoto reaffirms that he will continue to reject his father's power, Deku responds by pointing out that the power is Shoto's, not Endeavor's. Deku's words finally break through to Shoto, who remembers All Might's and his own mother's words that the Quirk isn't as important as the person who wields it and that it's okay for Shoto to be who he is and be a hero.
When Shoto tearfully accepts Deku's words and activates his flames, even Endeavor's celebrating doesn't faze the young Todoroki, who has grown one step closer to his dream by accepting his own power and himself. It's remarkable that Midoriya could instill such a powerful lesson in the middle of a fight that he's genuinely trying to win. It's a careful line to toe for Deku to help his opponent without becoming a hypocrite by allowing Shoto to win just to help him. Even All Might and Aizawa are astonished by Deku's willingness to destroy his own body, not only to win but to help his classmate.
The Todoroki family has, in many ways, become the emotional core of the series. Shoto could just as easily be the main character of My Hero Academia, as he has had to overcome more adversity than anyone else in his class. He had always been a powerhouse who coasted by on half of his power in an overly serious mood, and it was heartbreaking to discover what had made him this way. Shoto's journey on MHA has been equally, if not more compelling than even Deku's, and yet it never would have happened without Midoriya.