Shinobu Kocho/Synopsis

Past
Shinobu was born as the youngest daughter within the Kocho household, living alongside her mother, father and older sister Kanae Kocho. She was raised in a loving and caring household until her parents were slaughtered by Demons right before her and her sister's eyes.

Just when the Demon was about to take the lives of her and her sister as well, they were saved by the Hashira, Gyomei Himejima, who slayed the Demon. Now more determined as a result of the pain and suffering they endured, Shinobu and Kanae both promised to become Demon Slayers to protect each other, as well as prevent other people from enduring the same losses they had to experience. Eventually, after managing to move a boulder, they convinced Himejima to introduce them to a cultivator.

Later in her life, while accompanying her sister Kanae on a trip, the sisters encountered a young girl being led away as a slave on a bridge. Intrigued by her, Kanae took an interest and decided to take the girl back to the Butterfly Estate, against Shinobu's initial wishes. They eventually purchased the girl, named Kanao Tsuyuri, from her master and trained her within the Butterfly Estate to become the next Tsuguko.

At the age of 14, she became the master of the Butterfly Estate in Kanae's place, since Kanae died at age 17. Shinobu coddled the girls of the Butterfly Estate as if they were her own little sisters.

Natagumo Mountain Arc
Shinobu is present when Kagaya Ubuyashiki receives news of the situation unfolding at Natagumo Mountain, and is given the order to travel there and assist the lower-ranked swordsmen. Acknowledging this, the Hashira states that it would be great if everyone could get along, regardless if they are human or Demon, and asks Giyu Tomioka if he agrees.

Much later, Shinobu appears before a heavily injured Zenitsu Agatsuma, greeting and asking him if he is alright. She then suddenly appears behind the daughter member of Rui's Demon Family, inquiring if the strings came out of her palms, wishing the creature a good evening, and commenting on the beauty of the moon that night. Startled, the Demon attacks the Demon Slayer with her strings, but Shinobu dodges them all effortlessly. Drawing her sword, Shinobu dryly comments that this attack means that the Demon doesn't want to get along with her.

The daughter Demon quickly begs Shinobu for mercy, stating that she would be killed if she disobeyed Rui. Shinobu, sympathizing with the creature's plight, says that she will cooperate with the Demon if she answers a few of Shinobu's questions, the first of which being how many people she had killed. The Demon's answer is five, but Shinobu assures her that she doesn't have to lie, complimenting her string technique from earlier, and the Demon corrects her answer to eighty humans. Despite the creature's stubborn denial, the swordswoman notes that both of them came from the west side of the mountain, and, on that side, she had found forty of the Demon's cocoons. Shinobu adds that she isn't angry, but only trying to be as accurate as possible. When asked what the point of checking this information is, Shinobu tells the elder daughter Demon that in order for them to be friends and to satisfy those who have died, she will have to endure punishment, explaining in gruesome detail what she had in mind for this, and adding that the creature won't die from it, so there will be no aftereffects.

Enraged, the Demon attacks Shinobu again, but the Demon Hunter quickly bypasses her, simultaneously landing her Insect Breathing, Butterfly Dance: Caprice attack on the creature. She laments the Demon's poor choice, turning and subsequently watching as the creature collapses. Shinobu tells the creature not to let her guard down just because she can't cut the Demon's head off since, she explains, that she utilizes poison as her weapon instead. Shinobu then introduces herself as the Insect Hashira of the Demon Slayer Corps, stating that, although she may be the only one among her order to not possess the ability to cut off a Demon's head, poison that can kill the creatures is still a potent tool. She then apologizes, realizing that the daughter Demon is already dead and could not hear her explanation.

Shinobu then proceeds to cut open the Demon's silk cocoon, freeing Murata. She asks him if he is alright, and he asks what happened to the older sister Demon, to which she answers that she had killed the Demon with poison from the wisteria flower, commenting afterwards on how lucky he is for only having his clothes melted off by the creature's attack.

She later attempts to attack Tanjiro Kamado and Nezuko Kamado, but her attack is deflected by Giyu. She questions his interference, noting that if he continues this course of action, everyone would hate him. The Insect Hashira asks her fellow Demon Slayer to get out of the way, apologizing to him when he replies that he isn't hated. She then turns her attention to Tanjiro, telling him that he is protecting a Demon and that he should get away from her. The young Demon Slayer exclaims that Nezuko is his sister, causing Shinobu to take pity on her and plan to kill her with a toxin that inflicts no pain.

Giyu then instructs Tanjiro to run, which Shinobu notes to be a violation of Demon Slayer's conduct. Later, while being restrained by Giyu's arm, she laments that she had been in the right to come kill Demons and therefore had broken no rules, but noted that Giyu had, asking him what his intent was. Her fellow Hashira remains quiet, prompting her to angrily ask him to say something. Giyu replies that it had all started two years ago, causing Shinobu to note that the length of time was a problem and wonder if he was holding a grudge because she had said he was hated. She then extends a blade from her right shoe and prepares to attack Giyu, only to be stopped by an important message from a crow which said that Tanjiro and Nezuko are to be restrained and brought headquarters. Later, at the headquarters of her order, the Demon Slayer stood alongside her fellow Hashira in front of a restrained Tanjiro.

Rehabilitation Training Arc
She quickly informs the confused youth where he is and that he is on trial for violation of Demon Slayer conduct. When Obanai Iguro points out that Giyu Tomioka had also committed this crime and asks how they are going to deal with him, Shinobu tells him that they will think of a punishment for him later, since she is more interested in hearing Tanjiro's story. She gives the youth some water when he starts coughing, asking him to tell them his story, and also informing him that the water contained a painkiller. Shinobu tells him not to strain himself, as his injuries are still present. She then listens quietly as Tanjiro explains his sister's circumstances.

Shinobu continues to listen to Tanjiro's story, but his dialogue is interrupted by the sudden appearance of Sanemi Shinazugawa, who grabs Nezuko's box. She warns her fellow Hashira not to act on his own, but he ignores her warning, stabbing the trapped Demon with his sword, much to her displeasure. She then watches as an enraged Tanjiro charge the Wind Hashira, and afterwards looked at an apologetic Mitsuri Kanroji. Shinobu's leader, Kagaya Ubuyashiki, then arrived, causing her and her fellow Hashira to bow in respect. Kagaya then asked for them all to accept Tanjiro and Nezuko, surprising Shinobu, who remained silent as her fellows argued over the decision, and as Kagaya's assistant read Sakonji Urokodaki's letter.

Shinobu continues her silence through even more arguments, but is shocked as her leader revealed that Tanjiro had come into contact with Muzan Kibutsuji. She and her fellow Hashira are then halted from even more debating by a simple gesture from their leader, with the Insect Hashira remaining silent as Kagaya explains more of his reasoning for pardoning Tanjiro and Nezuko. Shinobu then cautions Tanjiro from using any of his breath techniques while pinned by Obanai, as his lungs might explode from the pressure. She calls out his name in alarm as he ignores her advice and tries anyways. After the incident with Sanemi and Nezuko is resolved, she listens quietly as Kagaya explained the dedication of the Hashira to Tanjiro.

With everything resolved, Shinobu suggests they take care of Tanjiro over at her place, instructing the Kakushi to do this, and then waits for Kagaya to start the Hashira meeting. After the meeting has ended, she visits Tanjiro and his friends at the Butterfly Estate, asking them how they are doing and instructing them to begin their Rehabilitation training.

Infinity Castle Arc
Inside the Infinity Castle that Muzan Kibutsuji had created after Oyakata's suicidal move, Shinobu enters a room and discovers Doma eating a group of his own female disciples. When he finally notices her, Doma reacts with delight at having another meal walk right into his room, and thanks Nakime. One of his disciples, still alive, begs Shinobu to save her, and Doma, irritated by this, attempts to finish her off, only for Shinobu to jump in and save her. She asks the young woman if she is alright, but before she can answer Shinobu's question, the young woman explodes and dies right in front of her eyes.

Angered by this, and Doma's insistence that he saved the girl by killing her, Shinobu notices a pair of sharp fans that Doma uses as his main weapon, and angrily inquires if he remembers the haori that originally belonged to her elder sister. Doma finally remembers her by the butterfly wing design haori that Kanae once wore, and playfully expresses his disappointment at not being able to eat Kanae due to the sun rising, which further angers Shinobu. The Insect Hashira swiftly launches an attack at him using her Insect Breathing, Dance of the Bee Sting: True Flutter to inflict a powerful stab directly in Doma's right eyeball, which impresses him since he couldn't block it.

Although he is initially dismissive of her, since he correctly guessed that she lacks the physical strength to cut off a Demon's head, he becomes excited upon learning that Shinobu's true strength lies in poisoning her opponents. Shinobu hopes that the poison will be effective enough to kill him, but then learns, much to her disappointment, that Doma had already received information regarding her poison from her battle against the Spider Family of Lower Rank 5. Doma manages to break down and render her poison non-lethal, healing himself from her attack. She is further backed into a corner due to Doma now rapidly developing antibodies and adjusting his body against her poison so that, after a mere five slashes and injections of poison, he is now entirely resistant to it. Also, due his Blood Demon Art of frozen mist, it is becoming increasingly difficult for Shinobu to breathe.

Now hedging her bets on injecting a large dose to kill him by using a six stab attack, Shinobu strikes him using Insect Breathing, Dance of the Dragonfly: Compound Eye Hexagon and successfully hits him. However, as she attacks him, he simultaneously attacks her, cutting both her collarbone and ribs and puncturing one of her lungs. Finally near her wits' end and almost losing any hope of victory, Shinobu attempts to draw strength from replaying her older sister's words of encouragement in her head. Shinobu then prepares to strike at Doma again, despite her serious injuries and the immense pain she was in, and attacks him using Insect Breathing, Dance of the Centipede: Hundred-Legged Zigzag, to confuse him. She strikes Doma directly through his neck, impaling him and sending him flying towards the ceiling. Exhausted and wounded, Shinobu is triumphant upon seeing Doma being poisoned and seemingly dying from her attack.

However, Doma recovers almost instantly from her attack, by which Shinobu is further enraged. Now exhausted, fatally injured, and dangerously near death, Shinobu is caught by Doma as they fell down from the ceiling. He embraces her in a bear hug and begins mocking her and calling her entire attempt to defeat him a waste of effort, assuring her she will live peacefully as a part of him, and mockingly asking her for her last words. She spitefully curses him as he begins to kill her.

In the end, she is absorbed by the Upper Rank, just as her disciple Kanao Tsuyuri arrives at the scene. Her death causes Kanao to go berserk in order to try and save her, only to be repelled by an irritated Doma, who tells her not to interfere when he's in the middle of absorbing someone. He successfully devours Shinobu's body until her butterfly-shaped hair piece is the only thing left of her.

It later turns out that she did predict her death at Doma's hand. Thus, with the help of Tamayo, she had began to intake and absorb wisteria flower poison regularly for over a year in the hopes that, if Doma consumes her, he will also devour thirty-seven kilograms worth of wisteria poison, which is nearly seven-hundred times the lethal amount. She hoped this would be enough to kill the Upper Rank, or at least weaken him enough for him to be slain by her allies later. Ultimately, Shinobu's plan works out, as Kanao, along with Inosuke Hashibira, manages to sever Doma's disfigured head from his body, fulfilling her revenge at last.

Inside the Limbo, Shinobu and Doma's head are conversing with each other. Doma finally shows emotion by saying he has fallen in love with Shinobu, and he proposes that they go to hell together. She declines cruelly, with a smile.

Shinobu is last seen with her sister, Kanae in giving their blessing to Kanao, before happily reuniting with their parents in the afterlife.

Two girls seen as the reincarnations of Shinobu and Kanae are seen attending an all girl's school in future Japan.