Rei Todoroki/Synopsis

History
Rei was born in the Himura family. When she was a young woman, Enji Todoroki proposed to her family to marry her. The family expressed great joy and was honored in being reached out to by the man who was said to be the next candidate for Japan's No. 1 Hero. Rei knew it was a Quirk Marriage, but married Enji for her family's sake. Rei showed a cold and distant demeanor, but when they were walking through the garden, Enji noticed that she was observing some flowers in particular, and asked her if she liked them, to which she answered yes.

Enji sought with that marriage to have a son who would inherit both his Hellflame Quirk and Rei's Frost Quirk. Their first son, Toya Todoroki, did not meet those requirements, but was born with a firepower greater than his own, so Enji decided to train him anyway. Even so, he still sought a child with a dual fire and ice Quirk, and according to Enji, Rei wanted more children, believing they could encourage each other, which ultimately led to Fuyumi's birth, though she was only born with her mother's ice Quirk.

Despite the fact that neither child bore the ideal Quirk Enji was hoping for, there were minimal problems in the family situation, as Enji was happy with the life he had, training Toya due to his potential, and Rei appeared to have had a relatively happy and stable relationship with her family. However, the situation changed when the hair of their firstborn began to bleach and his own Quirk burned his body. Enji suddenly stopped training his son Toya, telling him it was for his own good. Rei and Enji went to the hospital to find out what was happening to him. They were informed that Toya took after his mother physically, which meant his body was meant to withstand freezing temperatures and not the flames of his powerful fire-based Quirk.

Unfortunately, Toya refused to stop training, and would continue to do so on his own every time his father refused, getting more and more burns. As if this wasn't enough, Enji decided to keep trying to have a child who would inherit the two Quirks. Rei told Enji that having more children would be too cruel, especially since Toya knows what he wants from his children. Enji tells her that no matter what he says, Toya wouldn't listen, as his son inherited his stubbornness. He tells her it is the only way to make him give up because he would never be able to surpass All Might.

This ultimately led to Natsuo's conception, which also did not meet their requirements. This whole situation would begin to affect Rei psychologically, while Toya also started falling into despair. Several years later, she gave birth to Shoto, who inherited the Half-Cold Half-Hot Quirk that Enji envisaged.

Toya struggled to accept that his youngest brother would be the one to surpass All Might, so he continued training his Quirk more intensely without caring about the burns. This caused him and his father to have an argument at home, which Rei witnessed while carrying an infant Shoto. Enji asked his son to give up his dreams once and for all, telling him that there are more things beyond the world of heroes, with Toya replying in despair he cannot as he was the one who lit those ambitions in him. He told him to look at him as he charged with his flames activated at his mother in order to attack Shoto.

Enji was able to prevent something bad from happening, but this incident negatively affected Rei. That night, Enji decided they would not allow their other children to get near Shoto. He also told Rei he planned to hire a person to watch the kids as he remains busy with hero work, but asked her to never let Toya out of sight. Still affected by the incident, Rei told him that Toya just wanted Enji to notice him, but he replied back that all he can show him is the world of heroes. Rei, however, countered her husband, and scathingly told him that he's just running away from his problems.

When Shoto was five, Enji began to ruthlessly train him. Rei would attempt to intervene but was physically assaulted by him as a result. Despite this, she supported her son and encouraged him to push through the hard times. When Shoto expressed his worry over someday becoming a man like his father, she assured him that he could become whatever he wanted to be and that he was not bound to his bloodline.

Meanwhile, the situation with Toya was getting worse, as he used to sneak out to train his Quirk in secret. One day, Rei caught him preparing to go out into the mountain and begged him to play with his classmates, but Toya refused, saying he lived in a different world from them. Concerned that her son still wanted to be a hero, Rei advised him that must look beyond the hero world and explore other things. She wanted him to experience the real world and shape his personality.

Angry at his mother's statement, Toya yelled at her, causing Rei to freeze in shock at his intensity. Toya told her that he knew the truth, that her family sold her off to Enji because they were poor, so to him, she was guilty for why he was born too. Her eldest son's words affected her so much that she did nothing to stop him.

Time passed, and Toya's constant secret training made his Quirk evolve into something more powerful, being able to produce blue flames, so he was sure that his father would finally recognize his potential, but when he went to tell him, Enji was troubled and furious to find out that his training had also caused several burns to his body. Frustrated, Enji took his anger out on Rei and hit her for not stopping Toya, causing Shoto to yell at him to not bully her while his siblings listen on and Enji told Shoto to stay out of it. Remembering the words Toya said to her, she confessed to Enji that she couldn't stop him.

Enji's abuse made Rei start to lose her mind, and she began to see her husband's face in her children, finding it especially painful to look at Shoto because his left side reminded her of him. One day, while she was talking with her mother over the phone and discussing that she no longer had the stability to raise her son, she was startled by Shoto's sudden appearance at the door. Seeing his crimson hair, she snapped and threw boiling water from a nearby kettle over his head, severely burning his face. She immediately snapped back to reality and tearfully apologized to her son, using her ice Quirk to try and soothe the wound.

Shoto bore no ill will over this incident, instead directing it at his father, whom he blamed for his mother's suffering. Sometime after the incident, Rei was admitted to a psychiatric ward.

Shortly after this, the Sekoto Peak incident occurred. Because of his father's neglect, Toya lost control of his empowered Quirk, engulfing the entirety of the mountain in flames, and he apparently burned to death in the conflagration. After finding out about this, Rei had a relapse so bad that Shoto wasn't allowed to visit her for an unknown amount of time.

U.A. Sports Festival Arc
The day after the U.A. Sports Festival, Shoto visits his mother in the hospital. Rei is staring out the window and turns around when he enters. During Shoto's visit, she apologized through tears to him and smiled as Shoto told her he bore no ill will against her and knew she did not mean to harm him and he forgave her a long time ago. She then told him that she wanted him to be happy and save people, which allowed Shoto to finally leave his past behind.

Vs. Hero Killer Arc
Shoto continued to visit Rei on his days off every Sunday. On one Friday after school, after learning about the upcoming Parents' Day, he went to go visit her, thinking about the awkwardness over wanting to ask her about it, even though he already knows the answer. They're slowly able to communicate with each other, with Shoto talking about his recent experiences at school, when Fuyumi shows up, bringing her mom's washed clothes. She finds Shoto's Parents' Day request form, leading Rei to sullenly apologize that she can't come, disappointing Shoto. Fuyumi steps in to ease the tension, saying that she'll go in her place, even suggesting recording it for her to see, which slightly embarrasses Shoto, but he eases once he sees her improved reaction.

Pro Hero Arc
Her children Fuyumi and Natsuo would visit their mother in the hospital, which made her glad. Fuyumi leaves extra clothes for her mother since it will be cold next week to which Rei looks forward to since she loves winter weather and is glad to see that Natsuo is looking lively.

Natsuo compliments his mother's healthy complexion. Smiling, Rei comments that their brother Shoto regularly keeps in touch with her, sending her letters about his life at school and his friends. She is happy that he is doing his best to catch up with his classmates by completing the supplemental Provisional Hero License classes. Natsuo wonders why Shoto doesn't text her and Rei replies that she can't have phones at the hospital.

As they talked, Natsuo abruptly says that Endeavor officially was promoted to No. 1 Hero. Fuyumi tries to stop him since she does not want to talk about a sensitive issue in front of their mother, but Rei allows him to continue. Natsuo comments on how the outside world is unaware of the negligence and abandonment to which his father, and He can't stand that everyone behaves as if nothing had happened. Natsuo says that after ten years, Rei has still never received an apology from him, acting like he is leaving the past and his blood relatives behind.

However, Rei says that's not true and reveals that their father has actually visited many times, which surprises both Natsuo and Fuyumi. Rei says that on each visit he always brings Rei her favorite flowers. She says she told him one time, around when they first met, that she liked this type of flower. However, they still haven't met face to face because she's still too afraid of him and the doctors also said it is not a good idea. Despite everything, Rei knows that her husband isn't leaving everything behind, not his past nor his family and is trying to face them head on.

Endeavor Agency Arc
On New Year's Eve, Shoto once again goes to visit Rei, where they have lunch at the hospital cafeteria. He reflects on how it was the first in a long time since they've been able to eat together like that, noticing her steady improvement. He also tells her about finally getting his hero license, which she is incredibly happy and proud to hear about.

Sometime afterwards, Shoto receives a letter from her, hoping her son won't catch a cold in the upcoming chilly weather, saying how she's been going on more outings lately, and that the doctors' told her she could be discharged soon, thinking about wanting to live with her children again, to make up for past mistakes. Later, Enji reveals to Fuyumi and Natsuo his plan to help get a new home for them and their mother to live in together, knowing all the work Fuyumi has done to try and patch things up, while he stays at their old place to give them space.

Paranormal Liberation War Arc
In her room at the hospital, Rei is watching the news of Gigantomachia's rampage when the image starts to change and the video feed is replaced with an image of Dabi. Along with the rest of the world, she watches in horror as he reveals that he is actually Toya Todoroki, her eldest son, and has become a Villain who has killed more than thirty innocent people.

After hearing the news, Rei is released from the mental hospital and joins up with Fuyumi and Natsuo to meet Enji and Shoto in the hospital. As Shoto's classmates are consoling him, Natsuo and Fuyumi arrive while she appears in the back, slightly surprising Shoto.

The family then goes to meet Enji, who apologizes to all of them while expressing the pain in his heart. But before he can finish his sentence, Rei interrupts him and asks him about the pain in his heart, reminding him that the rest of his family have held the same regrets and guilt in their hearts for much more and much longer than he has. Enji is completely shocked at her arrival and asks what she is doing there. Rei replies that she is there to talk about their family and about Toya while carrying the flower Enji had given her before in her hand, upside down.

The family reminisce about the events in the past that led to Dabi's creation, where she tells Enji that he can't claim he is hurting more than anyone, and that he wasn't the only one who truly didn't see their son. She asks him why he never went to Sekoto Peak on the day of his "disappearance", with Enji admitting he didn't know what to say to him, which Rei responds that she didn't know either. Each of the family members state their regrets about not doing more to help Toya or potentially resolve things in the family (excluding Shoto).

Rei tells Enji that he isn't the only one responsible for Toya, that they are all responsible for the current circumstances, and that even if his heart is breaking, they will make him stand up. She says he has no choice but to fight Dabi. Enji is stunned at her resolve and asks if she truly is his wife. Rei goes on to say how Shoto has suffered more than anyone and had every right to resent her, yet still calls her "Mom", has made friends at U.A., and is doing all he can to save them now. That he is their family's Hero.

After the family comes to terms with everything, they resolve to work together to deal with Toya. They are then surprised by Hawks and Best Jeanist, who had been eavesdropping on the conversation, and also offer up their assistance. Rei gets on her knees and apologizes to Hawks for how badly Dabi had burned him, but he anxiously tells her not to worry about it, while being helped up by Best Jeanist. After hearing the revelation on Endeavor's past, Hawks asks Shoto if he also gave him his scar, but Rei immediately jumps in to take the blame for it, surprising Shoto. The discussion amongst the 3 Pros leads to Hawks asking Enji about "One For All", something Rei, Natsuo, and Fuyumi recognize overhearing from the media talking about it while trying to get into the hospital earlier.

U.A. Traitor Arc
Rei, alongside, Fuyumi and Natsuo, join the rest of the evacuated civilians to stay at U.A. for safety. Later, she is seen with her two children wishing Shoto luck as he and his classmates are about to head out of the school in preparation for the final battle.

Final War Arc
Rei is later seen in the U.A. Bunkers with Natsuo and Fuyumi, when they see Komari Ikoma watching over the Masegaki Primary School students, overhearing them talk about Shoto.