Natsuo Todoroki/Synopsis

History
Natsuo Todoroki was born the second son and third child of Enji and Rei Todoroki from their Quirk Marriage. Enji longed to have a child that could surpass All Might as a Hero, and therefore wanted to have an heir who would inherit both his own Hellflame Quirk and his wife's Frost Quirk. He was initially satisfied with his first child, Toya, however upon learning that despite inheriting a more powerful version of his Quirk, he also inherited his mother's weakness to fire, causing him to get burned anytime he used his Quirk.

In a twisted way to stop Toya from continuing to pursue this goal, he decided to have more children so that one will have the Quirk combination he desired, which he believed would break Toya's obsession. Natsuo was soon born, however just like his older sister Fuyumi, he only inherited Rei's ice Quirk, to his father's disappointment. Three years later his brother Shoto would be born, with the fire and ice Quirk that Enji wanted so much.

Sometime after Shoto was first born, Toya almost attacked the infant in a blind outcry for attention. He was stopped before he could harm anyone, but because of this incident, Enji forbade his older children from approaching Shoto. Natsuo and his siblings were raised separately from their youngest brother. By extension, Enji distanced himself to focus on his heir, entrusting Rei and hired carers to raise his other children.

Years passed and the three siblings grew up playing together. When Natsuo was around eight, he overheard Enji telling Shoto to not look at his siblings and they didn't belong in the hero world. He'd watch his younger brother being dragged away in confusion. Natsuo was prevented from knowing basic facts about Shoto, not knowing his favourite food until much later. Enji had begun abusively training Shoto and Rei's attention was forced away from her older children, as she had to intervene. Natsuo had slight envy, thinking Shoto was being favoured, though he overcame these feelings with time. As Rei became fearful of her husband, she struggled to look at her sons, as they physically resembled their father.

With Enji's increasing abuse and neglect, the family was falling apart at the seams. Toya had to use Natsuo for emotional support, crying and questioning his existence. Once, Natsuo grew weary of his brother's ramblings and suggested he talk to Fuyumi occasionally. Offended, Toya begged not to left alone by him as well. He claimed the family's girls were never expected to be heroes and only Natsuo could understand as a rejected candidate. Since then, Natsuo held nothing but resentment towards his father. To further motivate Natsuo's disdain for Enji, he would overhear Shoto and Rei's pained screams through the walls. Him and Fuyumi would hide in the corner, crying while Enji terrorized Rei.

Both Rei and Toya would soon reach their breaking points. First, Rei had a mental breakdown seeing Shoto's left side and poured boiling water on his face. His mother would be sent to a mental hospital. Some time after, Toya wanted his father to visit his training at Sekoto Peak and when he refused to show up, the teenager emotionally lost control of his flames. Toya's body, except his jawbone, couldn't be found after the forest fire and it was assumed he was completely incinerated.

His "death" devastated his family, and while it was an accident, Natsuo considers his father responsible, since Toya's training was motivated to gain Enji's acknowledgement. Toya's "death" worsened Rei's mental state and lengthened her stay at the hospital. Without their elder brother or mother around, Natsuo and Fuyumi were only left with each other.

Enji remained obsessed with isolating and training Shoto, neglecting Natsuo for the remainder of his childhood. Natsuo barely saw his father around, considering him a stranger and was apathetic towards him in turn. When their housekeeper wasn't available, the two took turns to cook. Natsuo wasn't sure if Enji and Shoto were served his cooking, since they never eat at the same dinner table. Fuyumi volunteered to take most of the housework, honing her cooking and ensuring everyone's general wellbeing. As they reached adulthood, Fuyumi convinced her brother that she could handle the family's circumstances and he should go out to pursue his own goals. So Natsuo left the household to study at college for a medical welfare degree, and eventually got himself a girlfriend as well.

Pro Hero Arc
Natsuo and Fuyumi visit their mother in the hospital. He tells his mother that Endeavor was promoted to No. 1 and that he still cannot forgive his father for how Enji treated the family. He is surprised when his mother mentions the latter visits her and left her flower. He is told of his father is dealing with an internal problem.

While leaving the asylum with Fuyumi, the siblings watched a news report of their father dealing with a special Nomu called Hood. He was horrified to watch as his father was overwhelmed by a villain's attack. Natsuo continued to watch the broadcast wondering why Endeavor continued fighting. He frantically stated that he should just give up and retreat-like he did with the children he had. Fuyumi told him their father is the person who is too stubborn to ever do so. Not without great difficulties and ended up seriously injured, Endeavor manages to defeat Hood.

At his family home, Natsuo eats dinner with his sister and brother Shoto before their father arrives. Seeing him, Natsuo glares at him, especially at his scar, before Fuyumi tells them to at least put in the effort to talk. However, Natsuo gets up to leave as Enji tells Natsuo to speak up and the latter confronts his father on everything he's done, even blaming him for what happened to his brother Toya. Natsuo continues his rant about not knowing much about his brother Shoto because of him and ending it by saying he's incapable of change, only to be surprised by Enji stating he will face his past to atone before Natsuo leaves.

Endeavor Agency Arc
Natsuo is present at the dinner, Fuyumi held for Shoto and company. When Izuku Midoriya praises the food Fuyumi made, Natsuo says that Fuyumi has been doing all the cooking ever since their maid hurt her back and retired. Fuyumi then revealed that Natsuo also did some cooking as well, which surprised Shoto. Though Natsuo then states that since he over-seasoned the food, Endeavor made him stop, though Endeavor apologizes for not knowing prior.

After Natsuo finishes, he quickly leaves, still unable to sit near his father. While the others were cleaning up, Izuku asks Katsuki if he knew about Shoto's past, to which he reveals he was listening when the two of them were talking during the U.A. Sports Festival. While getting ready to leave, Natsuo overheard Izuku tell Shoto that he feels he's getting ready to forgive Endeavor, as he feels that if Shoto truly hated him, it would be fine to not forgive him, but Izuku voices his thoughts on that Shoto is a very kind person waiting for the right moment.

While outside, Natsuo is captured by the villain Ending. Natsuo is brought to the roads where Ending challenges Endeavor for a previous loss at his hand or else his son dies. Held in the grasp of Ending, Natsuo is used as a shield by the villain, which halts Endeavor from attacking without hurting Natsuo. Soon, Natsuo is liberated by Katsuki Bakugo who safeguards him while Izuku and Shoto defeat Ending. Natsuo is then embraced by his worried father.

Dazed from the attack, Natsuo is asked by his father if he's hurt, while Natsuo only mentions how hot Endeavor's grasp is. Natsuo soon breaks free of Endeavor's grasp, as Endeavor reveals that he stopped to think in that moment fearing that if he were to save him, then Natsuo would never speak to him again. Natsuo hears his father confessed that he never meant to neglect him and Fuyumi all those years, but acknowledged that he failed to take responsibility by running away from them. He also acknowledges that he feels it's his own fault for Toya's fate. Natsuo tells his father he doesn't care, for he heard everything from Toya growing up and declares he will never forgive Endeavor because he doesn't see himself as kind as Shoto or Fuyumi.

Natsuo hears Endeavor state he still came out for Fuyumi and Rei's sakes and that he was trying to respect the feelings of his sister who is trying so hard to fix the family that Endeavor broke, signifying that Endeavor sees Natsuo as kind enough. Endeavor then states that it's okay if Natsuo doesn’t forgive him because he's not looking for it, he just wants to atone for his mistakes. Breaking into tears, Natsuo tells him that Fuyumi had been so happy lately, but every time he looks at him, he thinks of everything in the past. He questions why he has to be the only one to try and proactively change and what exactly will Endeavor do to atone.

After Ending is detained, Natsuo thanks his brother, Izuku, and Katsuki. He asks Katsuki what his Hero Name is. Katsuki tells him that he picked it but won't reveal it to them.

After returning home with his father, Natsuo is asked by a frantic Fuyumi if he was okay after being attacked, to which he confirms because Shoto and his friends saved him. He soon listens as Endeavor speaks to Fuyumi about the home she is trying to build for their mother to return and how all he could do was rely on her. He then declares that he will have a new house built in a more convenient location for her and Natsuo where she can welcome their mother back to. When Fuyumi questions what he'll do, Endeavor reveals he intends to stay at the abode and live alone, as he realizes that the only thing he can do to help his family to take himself out of the equation.

Paranormal Liberation War Arc
The day the raid against the Paranormal Liberation Front takes place, Natsuo goes to his classes, being accompanied by Fuyumi. She informs him that their father contacted her to say he won't be able to talk for a while due to work. Natsuo thinks back to Endeavor's battle in Fukuoka, hoping things don't turn out like that.

For the next couple hours he is in class, completely unaware of the battle taking place in Jaku City between the heroes and villains. After class is finished, he watches on his mobile phone Dabi's confession that is broadcasted to the world. Natsuo is horrified by the revelation that his older brother Toya is still alive and has become the villain Dabi.

After the epic battle had come to a conclusion, Natsuo, along with his sister Fuyumi and his mother Rei, go to Central Hospital to visit his wounded little brother. Shortly before entering, dozens of journalists approach them to ask about the latest events related to Endeavor and Dabi and "One For All", but they ignore them and continue on their way. A doctor informs them of Shoto's condition before going into his room. They enter to see Shoto recovering and being comforted by several of his classmates, where they introduce themselves and inform them of Shoto being unable to speak due to his burns.

Shoto is surprised to see Rei among them, after a bit of talking amongst themselves, the four decide to visit Enji. They awkwardly walk in on Enji breaking down, causing Natsuo to bluntly ask his father on why he is crying. Enji starts apologizing profusely, saying that his regrets and guilt are too late to matter, but before he can say something about his heart, Rei comes in asking about it herself. She also tells Enji that she and her children have been bearing those feelings of guilt and regret much more than he has. Natsuo watches as his mother tells a surprised Enji that she wants to talk about their family, and about Toya.

After the family reminisces on Toya, Natsuo says Enji is the root cause for Toya's descent into villainy, though Natsuo also takes some responsibility for not acting and speaking against his father when he was younger and maybe Toya would have never become Dabi. As they converse, Hawks and Best Jeanist arrive and revealed they overheard and wish to lend their aid in stopping Dabi. After watching his father cry again, Natsuo reminds him that he's only helping until Toya is stopped, as Enji is nevertheless grateful and continues crying while replying that he understands.

U.A. Traitor Arc
In the aftermath of the Paranormal Liberation War, All For One has escaped from Tartarus, and proceeded to break into several more maximum security prisons, liberating the inmates. Due to the chaos inflicted by Gigantomachia and the mass breakout of prisoners, the whole country entered a state of total chaos and anarchy. In addition, many heroes resigned and called it quits because of the massive criticism of their work, and the destruction spreading unchecked.

Because of this, Natsuo and his family were forced to move into the evacuation shelter at U.A. When his youngest brother, Shoto, is moving out of U.A. for good, he, Fuyumi and their mother came to wish Shoto luck in stopping the League of Villains.

Final War Arc
With all the heroes fighting the army of villains in the all-or-nothing Final War, Natsuo stays at the Underground Evacuation System beneath U.A., alongside Natsuo and Rei, where they see Komari Ikoma watching over the Masegaki Primary School students. Sometime later, the moving segment they are in suddenly stops and the lights go out, due to the influence of one of All For One's sleeper agents, causing Natsuo to protect his sister and mother, worried about what is going on.

With all of the heavy fighting going on due to the interference of the spies, the foundations of the blocks begins to collapse, so Gunhead orders the civilians, including the rest of the Todoroki Family, to quickly evacuate to the surface as the shelter continues to crumble apart around them. They all make their way outside, with U.A. robots there to let the civilians evacuate to wherever they want to go. However, just outside, they all bare witness to the immense heat and imminent destruction caused by Dabi's Blueflames, who unbeknownst to them, is on the verge of exploding and taking out everyone around him.

Natsuo and Fuyumi are shocked when they see their mother break away from them, and after she tells Natsuo to take care of his sister, commands the robot to take her into the center of the storm, where Endeavor and Dabi and currently fighting. The children follow their mother into the battlefield, where they see her using her Frost Quirk to attempt to shield herself from the intense heat, while also trying to cool Dabi down. They follow shortly behind her, using their Quirks to reach the rest of their family.

After Rei apologizes to Dabi, he recognizes Fuyumi and Natsuo, causing Rei to turn around and realize they followed her. She yells at them not to come, but Fuyumi tearfully replies she can't take anymore loss. She cries out to Toya not to take everyone down with him, not baring to lose anyone else. Natsuo then thinks back to his childhood days with Toya, and yells at his "idiot older brother" to stop causing so much trouble. The three Todorokis continue to blast their ice towards Dabi, in hopes of attempting to cool him down. Despite their attempts, they are unable to prevent the imminent explosion as the inferno sphere starts to expand further and further around them.

Just then, Shoto enters the vicinity to the rest of his family's surprise, having blasted all the way over to Gunga from Kamino to help. He surpasses his limits and unleashes his Phosphor-powered Great Glacial Aegir, completely consuming the inferno in his ice, preventing Dabi's self-destruction and causing the fire to dissipate and burn out.

Natuso, Fuyumi, and Rei try to recover from their heat and frost burns, with Natsuo holding onto his mother, while Shoto stands over the crisped and partially frozen Dabi. Shoto admits that it is good they were there to help cool him down because his Great Glacial Aegir might not have been enough to stop it, since Dabi's Blueflames have been increasingly getting hotter, far beyond his reach and figuring he was not the "masterpiece creation" after all.

Dabi's body begins to freeze from the inside out, and he can only croakily vent out to everyone, including himself, to just die. Seeing this, Natsuo wonders out loud what comes next, as all that awaits for them now is pure hell. As Dabi lays there, a severely wounded Endeavor crawls toward his son and holds onto him, remorsefully apologizing to Dabi for not going to Sekoto Peak. Dabi responds that he hates him and his family, and Endeavor continues to break down, saying to let him have it, and starts to repent for his sins by apologizing to Natsuo for neglecting him, as well as everything else he did to Rei, Fuyumi, and Shoto.

Shoto eventually collapses due to over exhausting himself, while Natsuo and Fuyumi sense the threat of the Twice Double swarm rapidly approaching.