Himiko is the eldest daughter of the Toga family. When she was a child, likely due to her Quirk, Himiko showcased a rather disturbing and morbid interest in blood. She once brought a dead, bloodied bird to her parents and cheerfully asked them if it was "pretty," which in turn scarred and disturbed them. Disgusted with her behavior, her parents tried to suppress it from a young age by putting immense pressure on her to be "normal," which she then took to heart. Since then, she began to repress and hide her "abnormal" tendencies and began to act like a "ideal young school girl expected of society." She successfully hid this side of herself so thoroughly that by the time she was middle school student, Himiko was known by her classmates as a "cheerful and well-behaved girl," becoming a normal student with many friends.
However, this all changed when she witnessed a boy attending her school named Saito, fighting at school and getting covered in bruises and blood. Awakening to her repressed "abnormal" feelings and tendencies, Himiko experienced what she believed to be a crush on him. Sometime later, Himiko had seemingly succumbed to this infatuation and attacked him using a box cutter. She stuck a straw into his wound and began sucking his blood while crying and, according to a passing classmate who had witness the assault, had a look of ecstasy. Soon after, she disappeared and hid from both the police and Pro Heroes, as she was now a wanted suspect due to the attack, and later became the prime suspect in several murders involving bloodletting. However, Himiko managed to successfully evade and escape them all, until she officially joined the League of Villains.
Three days following the Hero Killer's arrest, Himiko is first seen skipping down a dark alleyway. She has headphones on and listens to the news report on Stain's capture. Later on, before she moves on towards the League of Villains, Himiko is seen blushing in front of a man that is bleeding in an alleyway.
Giran brings Himiko and Dabi to the League of Villains. Himiko is excited to meet "the hand guy" and asks him to let her join the group. Tomura Shigaraki wants them both thrown out, but Kurogiri convinces him to give them a chance. Giran introduces Himiko as a cute high school girl who was the suspect in a series of murders by blood loss and whose appearance and name has been kept from the public. Himiko goes onto present herself and says life is too hard and she wants to make it easier to live. She goes on to say that she wants to be like Stain, she wants to kill Stain, and she really wants to join Tomura's group.
Tomura asks Giran if she is crazy. Giran replies she is competent enough to be of use and then introduces Dabi. Dabi questions the League's commitments to the Hero Killer's mission because he cannot believe they would let someone as crazy as Himiko in if they are. She is taken back by his comment and Tomura defends her by saying at least she had the decency to introduce herself.
After arguing with Dabi, Tomura takes offense to the recruits' loyalty to Stain and attacks them. Himiko draws her knife and counterattacks, but Kurogiri uses his Quirk to stop the fight. Tomura storms out and Kurogiri asks the new recruits to be patient because an answer will come for them soon. Himiko mentions that she thought Tomura was going to kill her.
Himiko is eventually recruited to the League of Villains and assigned to the Vanguard Action Squad. Tomura acquires equipment for the team and has them pick it up at an unknown warehouse location. Himiko announces there is enough gear for everyone and they should bring it along on their mission. Muscular adds they need to hurry up, but Mustard disagrees because the team has been ordered not to rush or do anything too flashy. Dabi proclaims that their mission will be a warning shot that will tear down false heroes from their shining pedestals and drag them back to earth in order to create a new future for the world.
The next day, Himiko and six other villains secretly arrive at the Wild, Wild Pussycats' forest reserve, where U.A. High School students are training. The Vanguard Action Squad observes the campsite from a high vantage point. Himiko puts on her new gear and complains about the way it looks, stating that it is not cute. Mustard argues that she should be concerned about its functionality. She ignores him and says that it is not stylish enough for her.
The Vanguard Action Squad begins their assault the next evening. Himiko finds Ochaco and Tsuyu walking through the forest and cuts Ochaco's upper left arm open. The wound is not large enough for Himiko to collect a lot of blood. She mentions that she normally sucks it straight from the wound. Without not enough time to do that, Himiko arms herself with the blood-draining devices from her new equipment. Tsuyu flings Ochaco away after Himiko rushes at them. Himiko cuts Tsuyu's tongue and notices that Ochaco called Tsuyu "Tsu-chan". Himiko likes this name and declares she will call Tsuyu that too. Tsuyu refuses her and says only her friends can call her by her nickname. Himiko pins Tsuyu to a tree by her hair and says that they must become friends if that is the case.
Ochaco returns to save Tsuyu and Himiko stabs at her. Ochaco evades before using martial arts to slam Himiko and restrain her. Himiko starts talking to Ochaco, noting that they have the same smell because they are in love with someone. She goes on to explain that someone who is in love tries to become the person they love. Himiko says she loves people who are cut up and bleeding and that it is fun for the girls to be talking about their crushes. This distracts Ochaco long enough for Himiko to stab her leg and drain her blood with a needle.
Other students arrive at the scene, so Himiko quickly flees, fearing that taking on a large group will get her killed. Before she fully retreats, Izuku Midoriya catches her eye. Ochaco wants to pursue Himiko, but Tsuyu stops her because they do not know anything about the villain or her Quirk.
Following Mr. Compress' successful capture of Katsuki Bakugo, Himiko regroups with the remaining villains. Dabi inquires about Himiko's mission to collect three blood samples. She admits she only got one person. Twice asks why she appears to be so upbeat after failing. Himiko replies that she has made new friends and found a boy she is interested in.
The same boys who interrupted her fight earlier abruptly arrive after tackling Mr. Compress to the ground. Himiko jumps on top of Izuku as he falls to the ground and tries to stab him, only for Mezo Shoji to push her away from him. Himiko threatens Mezo for getting in her way. Kurogiri arrives to warp the villains to safety. As Himiko enters a portal, she apologizes and says goodbye to Izuku, hoping to see her crush again another day.
Himiko returns to the hideout with her comrades after successfully kidnapping Katsuki. She listens as Tomura and the others explain why the League exists to destroy Hero Society and they try to convince him to join. Katsuki refuses and attacks Tomura, exploding the mask off his face. The U.A. student tells the League he wants to be like All Might and not the villains.
Magne comments that Katsuki is clever, but Dabi disagrees. Himiko simply adds that she'll stab Katsuki. Tomura tells everyone to calm down and not to touch Katsuki. He puts his mask back on and asks his master to lend him the ability to force Katsuki into submission. Suddenly, someone claiming to be from Kamino's pizzeria knocks on the door, confusing everyone, including Himiko. All Might abruptly breaks in the wall of the hideout alongside a team of heroes.
Kamui Woods restrains all the villains using his Lacquered Chains Prison. The Police have thoroughly investigated the League of Villains and discovered most of their identities. Himiko watches in horror as Edgeshot knocks out Kurogiri and the League loses any hope of escape. All Might and Gran Torino declare that it's over for the League.
Just when all hope is lost for the villains, a mysterious black liquid transfers a Nomu into the hideout. The same liquid warps the villains away and they re-appear by All For One at the Nomu Factory. All Might follows them there and All For One holds him off. He orders them to recapture Katsuki Bakugo before the heroes catch up with them.
Himiko and her allies ambush Katsuki and he avoids them using his explosions. Himiko uses her knives to try and cut Katsuki, but his explosions keep her back. Katsuki's classmates make a sudden rescue attempt that succeeds and he escapes the battlefield. Gran Torino arrives on the battlefield and knocks out most of the villains. Himiko is afraid she'll be killed or captured, but All For One uses Magne's Quirk to send everyone toward Himiko. She's afraid she'll get hurt from the impact, but everyone is drawn to her and they're all sent through a warp gate to safety.
The League of Villains recovers in an unspecified apartment, where Tomura swears vengeance for his fallen master. Himiko and the others sit in silence after their defeat.
The League of Villains regains their momentum and sends Himiko on a mission to infiltrate the Provisional Hero License Exam. She drugs Camie Utsushimi, steals her blood, and disguises herself as the Shiketsu High School student.
On the day of the exam, Himiko joins her "classmates" Inasa Yoarashi, Seiji Shishikura, and Nagamasa Mora as they introduce themselves to Class 1-A. Inasa bleeds after apologizing for being rude and Himiko is infatuated by the blood pouring down his forehead.
Toward the middle of the exam's first phase, Himiko confronts Izuku alone. She uses her acrobatic abilities and her stealth to catch him off guard and tags one of his targets. If she can tag all three, Himiko can eliminate Izuku from the exam. Himiko scolds Izuku for zoning out in the middle of a war zone. 
Himiko uses her ability to hide her presence to confuse Izuku and dodge his attacks. She sneaks up behind him and pins him to the ground with his arm behind his back. Himiko whispers into his ear and explains her stealth tactics and reveals it's not a part of her Quirk. She wants to know why Izuku wants to be a hero, but he doesn't answer and breaks free from her hold.
Competitors from Ketsubutsu interrupt the fight and Himiko disappears. She changes into Ochaco and pretends to be in peril so that Izuku saves her. When they're safe, Himiko tries to tag another one of Izuku's targets, but he sees through her disguise. Caught, Himiko changes back into Camie.
Himiko wants to know what lengths Izuku will go to be a hero. He says he would rather talk after the exam and demands she put some clothes on. Himiko swiftly attacks and scratches Izuku's face. She tries to keep attacking, but Ochaco and Hanta arrive to save their classmate. Himiko is forced to retreat and is dismayed she didn't get to talk to Izuku more. She tells Ochaco that Izuku really trusts her and then leaves the area.
Himiko manages to eliminate two students and becomes the 98th person to pass the first phase. She rejoins the Shiketsu students in the anteroom and Nagamasa scolds her for going out on her own. Izuku, Denki Kaminari, and Minoru Mineta stare at her from across the room and Himiko waves at them. This makes Denki and Minoru suspicious of Izuku after Hanta tells them about Camie's naked encounter with him.
Himiko sticks with her "classmates" during the start of the final phase of the exam, but leaves early under the excuse that she wasn't feeling well. She escapes without anyone ever suspecting her and receives a call while walking down an alleyway. The call is from Mr. Compress, who scolds her for not contacting her allies sooner. Himiko claims there's nothing to worry about because she's never been caught. Himiko sheds her Camie disguise and informs Compress that she got some of Izuku's blood.
Himiko reunites with the League of Villains at a secret unspecified warehouse. Twice brings them a new recruit, the young Yakuza Captain of the Shie Hassaikai: Overhaul. Himiko asks what a Yakuza is and Compress explains they're relics from a time before the age of heroes. Overhaul suggests the League of Villains work for him and they refuse.
Magne attacks him, but Overhaul abruptly murders her within seconds, shocking Himiko. Compress attacks and get his Quirk erased by a mysterious bullet, giving Overhaul enough time to completely destroy his left arm. Tomura attacks and kills Overhaul's mook who suddenly appears to protect Chisaki, and then several Overhaul's followers barge into the hideout, ending the battle. Overhaul decides to end the meeting and leave, wanted to continue with the negotiations once the League of Villains have cooled down.
Twice and Himiko want to avenge their allies and kill them, but Tomura orders his followers to stand down. Twice checks on Compress's condition and Himiko tells them they need to get Compress to a doctor. She is also furious over Magne's death and expresses her desire to avenge her.
Several days later, Tomura meets with Overhaul to form an alliance, on the condition that he tell her his plans. In return, Overhaul asks for Twice and Toga as proof of trust between the two factions. Tomura accepts, and later explains the situation to Twice and Toga.
Neither of them accepts this and Himiko confronts her masked leader. She spins around and tells Tomura that she joined the League because it makes her happy and easier to live in the world. Himiko turns her knife to Tomura's neck and demands to know why he would make her do something so unpleasant.
Tomura surprises Himiko by taking off his mask. He says they must do it for his sake and all of theirs. The Shie Hassaikai is trying to overtake the League of Villains and Tomura needs Himiko and Twice to do this to help the League. He trusts them to do their best and the duo is moved by Tomura's words.
Himiko and Twice are brought to the Shie Hassaikai Headquarters where they meet with Overhaul and all his main followers. He asks that they both explain their Quirks, but Himiko refuses to because she still hates the Yakuza. Twice agrees, but Shin Nemoto uses his Quirk to make Twice confess. This embarrasses Himiko, but suddenly she explains the details of her Quirk too. Shin uses his Quirk again to ask if Tomura planned on betraying them. Himiko and Twice both deny any plans of betrayal. Overhaul asks that, as wanted criminals, both the temps stay on base for the time being.
Sir Nighteye's investigation leads a team of heroes to the Yakuza hideout. Overhaul orders the temporary Yakuza to hold off the enemy to cover his escape. Himiko and Twice are forced to work alongside Mimic to take down Sir Nighteye's team. Mimic separates the hero squad from one another and Himiko ambushes Rock Lock. She stabs him through his hand, but he uses his Quirk to lock her knife in place. Rock Lock punches Himiko, but she turns out to be just a clone. The real Himiko wraps herself around Rock Lock's back and stabs him. The Lock Down hero asks why the League of Villains are attacking, but Himiko reminds him that she's a Yakuza now and incapacitates him.
Himiko ingests Rock Lock's blood and transforms into him. Izuku and Eraser Head break into the area and Himiko says an imposter attacked her. She gets close to Izuku and Eraser Head notices the knife wounds on Rock Lock's body. He erases Himiko's Quirk as she tries to stab Izuku. He recognizes her, much to her pleasure, but Eraser Head uses his Capturing Weapon to pull her away. Himiko wraps herself in the scarf and counterattacks by stabbing him in the shoulder. She gets away and Mimic helps her retreat behind a rock wall. Afterwards, while putting her clothes back on, she states that she's glad she came.
Twice is forced to retreat as well after Sir Nighteye destroys part of his mask. Himiko stops his panic attack by wrapping the exposed part of his face behind a cloth. She empathizes with him and recognizes that he feels horrible for what happened to Magne. Himiko and Twice remember that Tomura trusted them and they both decide to act freely and to do what makes them feel good. They berate Mimic and the Yakuza for being useless, throwing him into a frenzy.
Mimic starts distorting the cave and tries to crush the villains and heroes alike. Himiko decides to use the heroes to destroy the Yakuza as proper revenge. The heroes can't find Mimic's real body, but Himiko knows he's a weakling who looks down on people from above. Mimic gets angry and yells at her, giving the heroes an opening to defeat him. As Mimic falls defeated, Himiko and Twice wave goodbye to their rival villain.
From an upper floor, Himiko and Twice witness Mimic's arrest, and learn that Izuku, Shota, and Sir Nighteye went ahead of the group to stop Overhaul. Seeing that the heroes and the Police Force are gone, the two come out of hiding. While wanting to see Izuku badly injured again, Himiko wants to make Kai Chisaki pay. Twice whispers something into Himiko's ear, and she thinks that Tomura Shigaraki will be quite pleased with it. She hopes that whatever the conclusion is between the Heroes and the Shie Hassaikai, they will all be injured and tired at the end.
Himiko and Twice get above ground and try to devise a scheme to keep chipping away at the Yakuza. Himiko wants to kill Overhaul herself, but figures she won't get the chance. She transforms into Deku and leads Ryukyu's Squad right to Overhaul's battle with Nighteye's squad. They want to try and steal Eri, but the ensuing fight causes too much chaos and they're forced to hide.
Deku defeats Overhaul and the Shie Hassaikai are arrested and transferred to a villain hospital. Himiko relays this information to Compress and Tomura, who, along with Dabi and Spinner, ambush the transport on the highway. Himiko admits that Twice is the one who made the call because she was busy crushing on Izuku. She knows they were unable to capture Eri, but believes the League of Villains can still win by stealing the Quirk-Destroying Drug.
Prior to the Hero Billboard Chart JP, the League of Villains has seen better days. They've resorted to stealing from other criminals to stay under the radar and amass funds. One night, Tomura leads Himiko and the others into the house of the Creature Rejection Clan. Himiko and Compress start looking for valuables, upsetting the clansmen. The villains slaughter all of the CRC members and Himiko breaks one of her needles in the process. Compress suggests they call Giran to replace her weapons and his prosthetic, but Himiko asks where they're getting money for that.
The villains return to the hideout where Himiko and Twice rummage through the junk they collected from the church. Dabi returns and dissatisfied to find his colleagues doing nothing. Twice reminds Dabi that he cremates everyone he runs into and Himiko adds he's a bad judge of character.
Tomura says that it has been a month since Kurogiri was captured and he still hasn't been able to reach the Doctor. Himiko questions the importance of those statements and Tomura reveals Kurogiri went to retrieve a secret weapon while the Doctor plays a pivotal role in their operation. Himiko and Twice taunt Tomura for not denying he misses having Kurogiri around like a babysitter.
Spinner confronts Tomura over the state of the League but Himiko seems bored and mostly ignores it. Suddenly, a fierce rumbling shakes the hideout and all the villains rush outside. They are met with a giant behemoth of a man claiming to be looking for All For One's successor. He demands they prove worthy and easily overpowers them, wailing out in disappointment over their weakness.
The voice of the Doctor Tomura has been searching for plays over the giant's radio. He introduces the beast as Gigantomachia AFO's former bodyguard. Gigantomachia is upset at the disparaging difference between AFO's power and Tomura's. Dabi tries to prove the League's worth with a fire attack, but Himiko tells him it doesn't work as Machia bursts through the flames.
The Doctor plays AFO's voice to calm the giant and asks for a minute. Himiko replies a minute for what and Twice burps while he's annoyed. Himiko calls him gross for burping but black slime abruptly bursts out of all the villain's mouths before warping them to the Doctor's lair. He introduces himself as Daruma Ujiko and asks Tomura why he should receive help after the League of Villains has accomplished next to nothing.
Tomura reveals fragments of his past have left a hole in his heart that can never be filled. He wants to use that anguish to destroy everything that exists. Himiko appears to be confused alongside the other members listening to Tomura. She even asks if Tomura means to destroy everything they love but Tomura explains his allies are excluded, exciting Himiko.
The Doctor accepts Tomura but will only fully support the League after the villains reign in Gigantomachia and prove themselves. Dabi refuses to help, prompting Himiko to taunt him about his failed attack earlier. The Doctor transports everyone else back to Gigantomachia, where Tomura leads them with his restored confidence.
For the next month and a half, Himiko and company support Tomura as he fights against Gigantomachia for nearly 45 hours at a time. With what little funds Himiko received from the doctor, she bought a winter coat. While off-shift with Spinner, Himiko watches Tomura, Twice, and Compress lose to Gigantomachia once again. She comments that the "Future King" is in trouble.
Toasty, Himiko shares with Spinner that she slows down when she's cold. Spinner asks her why she's still with the League when no semblance of the Hero Killer remains within the group. She simply replies that she loves Stainy, along with Izuku and Ochaco. Himiko simply wishes to become everyone she loves. Spinner commends her for being such a free spirit.
After Gigantomachia falls asleep, Himiko checks on Tomura's condition. He's alive and believes he'll make the giant kneel before him soon. Their chat is interrupted by a mysterious call from the Meta Liberation Army using Giran's phone. Re-Destro explains the army has captured Giran and they wish to create a society where Quirks can be used freely. Compress doesn't see why the League would oppose that and Himiko asks him if they're going to lend them the League's reputation as they did with the Shie Hassaikai.
Re-Destro reveals he has an army of over 100,000 soldiers and a satellite tracker on the League. As a declaration of war, Re-Destro demands the League go to Deika City and signal the rebirth of the Army. Twice wants to rush in to save Giran, but Himiko reminds him their enemies might be lying about keeping him alive.
Tomura takes charge of the situation and proposes the League use the liberation warriors to wear down Gigantomachia, killing two birds with one stone. He leads them to Deika City where they regroup with Dabi. A mysterious person approaches and Himiko is the first to notice. She and her allies ready for battle, but the stranger reveals himself to be Slidin' Go: a Pro Hero aligned with the Liberation Army.
Slidin' Go escorts the League of Villains to two of the lead revolutionaries: Koku Hanabata and Chitose Kizuki. Koku, leader of the Hearts and Mind Party signals the start of the Meta Liberation Army's Revival Celebration. Dozens of citizens ambush the villains. Tomura orders his group onward to the tower where Re-Destro is holding Giran. Excited, Himiko starts to run but the ground beneath her explodes.
Chitose confronts Himiko, recognizing her for the string of bloodletting murders she's connected to. Chitose suggests a headline about how the high-schooler's fall into madness, but Himiko angrily rejects it.
Chitose proceeds to battle Himiko, attacking her in-mass with her comrades in order to corner her, all the while "interviewing" her on her reasons for becoming a villain and she proceeded on shedding light on Himiko's past prior to joining the League, and expressing extreme interest and curiosity regarding her reasons for abandoning her normal life, where and how she obtained her survival and combat skills and the reasons for Himiko's descent into madness, even going as far as using her own subordinates as human bombs in order to further corner Himiko and prevent her from transforming by detonating their ingested blood inside her body in order for their "interview" to go unhindered.
As Himiko attempts to escape, Chitose continues to goad her, promising to go public with the tragic story of Himiko's downfall in order to demonstrate the righteousness of the Army's objective. When Himiko transforms into Ochaco Uraraka, Chitose dismisses it as her final attempt to "look cute" before her death, but is caught off guard when Himiko activates Zero Gravity to levitate her into the air. Bewildered, Chitose assumes that Himiko's fear of death has allowed her Quirk to spontaneously evolve in power. When Himiko replies that she’s wrong and that Himiko only wants to "love" even more, Chitose begins saying that this would be her best headline ever, before Himiko deactivates Zero Gravity, sending Chitose and her henchmen plummeting bloodily into the ground.
Himiko manages to make her way to a shed away from the battlefield where she collapses due to her fatigue and blood loss. As she loses consciousness, she recalls the sensation of love, feeling closer to the people she "loves". Later, she is found unconscious by Twice, who upon checking that she is grievously wounded and won't wake up, breaks into an argument between his split personalities for a while: one dismissive about her critical condition and saying that Toga will die soon, while the other bursts into tears and wants to help her. Soon, they are surrounded by a group of "puppets" created by the Quirk of Tomoyasu Chikazoku. Twice panics when he finds that the puppets have his same face, reawakening his trauma of the clones he created with his own Quirk killing each other.
The unconscious and injured Himiko is slowly tortured by the clones, while Jin is forced to watch and injured. However, this brings a new rush of confidence from Jin who finally has confirmation that he is the real Jin Bubaigawara. Jin the generates a group of clones that break through Skeptic's puppets, saving Himiko.
Himiko is carried by Jin through the streets, as his clones cause chaos for the enemy.
Himiko is taken to a park, where Twice prepares to do a blood transfusion to replace her massive loss. Twice creates a clone of Himiko to do so, as Skeptic's puppets attack.
Once Re-Destro was defeated and bestowed control of the army to Tomura, Himiko ate sushi along with her comrades after the battle. Her injuries were tended to at a hospital and she is slowly recovering from her wounds. When Twice for mourns a picture of her, she berates him for his behavior since she is very much alive and the picture is creeping her out. During Re-Destro's speech, Himiko notes to Spinner on Tomura still having one of his signature hands and he tells her one hand survived. She and the rest of the League came on stage when Tomura announced the Meta Liberation Army and League of Villains will become the Paranormal Liberation Front (which Spinner and Re-Destro coined together), becoming one of its Lieutenants.
Sometime later, Himiko is shown to have recovered from her injuries and is present at Hawks's report of how Endeavor has taken on two interns. She muses on one of them being Izuku and dismisses Hawks after thanking him for a good job. Afterwards, she and her allies discuss the upcoming goal of the army that would take four months to put in motion. Himiko notes that Tomura will destroy everything after he gets a grip on his abilities.