History
Shinobu was born as the youngest daughter within the Kocho household, living alongside her mother, father and older sister Kanae. She was raised in a loving and caring household until her parents were slaughtered by demons, before her and her sister's eyes.
Just when the demon was about to attack her and her sister, they were saved by the pillar, Himejima Gyoumei, who slayed the demon. Determined by 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.
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 Tsuyuri, from her master and trained her within the Butterfly Estate to become the next tsuguko.
Personality
Shinobu is rather laid-back, always having a smile on her face regardless of the situation she is in. She seems to enjoy teasing others and can be rather sadistic about it, enjoying most notably to pick on Giyu Tomioka. Despite her relaxed exterior and her initial claim of wanting to get along with Demons, she can be rather cruel towards them, which is seen when she kills the Older Sister Spider Demon after giving her false hope of helping her and also attempting to kill Nezuko Kamado without hesitation. Later on, she is shown to have a more compassionate side towards both Tanjiro Kamado and his sister after hearing their full story.
It is later revealed that her outwardly calm and tranquil disposition is worn as a mask, as Shinobu holds an intense hatred for Demons due to the loss of her sister, Kanae Kocho, at a young age, along with the deaths of her parents, most of her Tsuguko, and the families of her apprentices at the Butterfly Mansion. This hatred is so strong that she is in a near-constant state of anger, which is sensed by Tanjiro Kamado when the two individuals hold a conversation. Her desire for revenge rendered her unable to live the normal life her sister had wished upon her, instead devoting the entirety of her energy to defeating Demons.
During her battle against Doma, Shinobu reveals that she also suffers from an inferiority complex due to her inferior physical abilities compared to her fellow Hashira, having been jealous of them for possessing taller or more muscular bodies than her and cursing her own for not developing further to make her more effective in combat.
Shinobu's younger self had a more brash and straightforward demeanor as seen when she and her sister rescued Kanao Tsuyuri, who she had a negative attitude towards raising. After the death of Kanae, however, Shinobu started outwardly behaving more like her sister and eventually developed her smile and attitude to match while internally holding in her rage.
Abilities and Powers
As a Hashira of the Demon Slayer Corps, Shinobu is a very powerful swordsman. Despite not possessing the physical strength to cut off a Demon's head common to that of an average Demon Slayer or even the superhuman abilities possessed by her fellow Hashira, Shinobu is nonetheless as dangerous and deadly as the rest of them.
Natural Abilities
Master Swordswoman: Being a Hashira of the Demon Slayer Corps, Shinobu is one of the most powerful and skilled swordswomen in the entire organization.
Medical Expertise: Despite not being as combat-talented as the rest of her fellow Hashira, Shinobu instead displays immense skill and mastery over medical and pharmaceutical fields to make up for her lack of natural-born combat ability, being highly knowledgeable about how to create various poisons and venoms using Wisteria flowers. She is capable of killing opponents within seconds, and even manages to create a poison strong enough to drastically weaken Doma, the second strongest Demon of the Twelve Kizuki. She possesses the necessary skills to slowly saturate her body with poison without negatively impending her own health, as well as the medical skills needed to counteract the venoms and poisons created by Demons. This is seen when she manages to undo the poison that is slowly transforming Zenitsu into a spider and restore him back to his previous human form.
Anti-Kibutsuji Drug: Upon teaming up with Tamayo and Yushiro, Shinobu was able to aid Tamayo in creating a successful, four-stage drug that would be used to significantly weaken Muzan Kibutsuji, even despite his immense physical resistance and abilities. The first stage, although unsuccessful on Muzan, is capable of turning a Demon back to a human.
Aging Stage: The aging stage was the second stage of the drug and an idea proposed by Shinobu herself. This stage aged its user at a rate of fifty years over a minute, which, in Muzan's case, successfully aged him 9,000 years over three hours. The side effects of this aging process caused Muzan to slow down enough for the Demon Slayers to continuously fight him.
Human Conversion Stage: After working with Tamayo, Shinobu helped her create the successful Demon-to-human conversion drug, a feat considered impossible. Both Muzan and Nezuko received the drug, but Muzan was able to decompose it and render it ineffective. However, Nezuko was able to revert to her human form and regain her memories upon receiving the drug.
Immense Speed: Shinobu has displayed almost superhuman levels of speed, being fast enough to easily evade and out-pace Demons, catching them by surprise. Doma, the Upper Rank 2, stated she might have been the fastest Hashira he had ever met.
Enhanced Strength: Despite being the smallest member of the Demon Slayer Corps and thus having the weakest swing strength due to her small arms, Shinobu instead displays powerful thrust and stab strength, as the other Hashira notes that a single thrust from her sword could easily pierce a stone boulder in half. Her thrusting speed is also noted to be the fastest among her fellow Hashira.
Swordsmanship
Unique Weapon: Shinobu uses a heavily modified katana made by Tecchin Tecchikawahara as her primary weapon. It is the same as any katana from the handle to slightly above the hilt, but above that, the weapon loses its blade and is replaced by a rod. It ends in a needle-like tip, resembling an insect's stinger in appearance and function. The "stinger" is designed for injection of Wisteria poisons into Demons, as Shinobu uses her medical expertise to overcome her relative lack of strength and inability to cut off heads. She has also modified the weapon's sheath, using it as a portable poison mixer and loader. She is one of five Hashira to wield a unique weapon, the others being Tengen Uzui, Mitsuri Kanroji, Obanai Iguro, and Gyomei Himejima.
Insect Breathing: The Insect Breathing is branched out from the Flower Breathing, which itself is branched out of the Water Breathing. While Shinobu may have been the only one of the Hashira incapable of beheading Demons, she is still just as deadly as they are. Using this unique Breathing, she coats her weapon with poison made from Wisteria flower and alters the mixture and composition of the poisons inside her scabbard.
Butterfly Dance: Caprice - Shinobu jumps forward towards the opponent and stings them multiple times with her blade to inject her poison.
Dance of the Bee Sting: True Flutter - Shinobu dashes at her target at an incredible speed and uses the momentum of her speed to then strengthen her single thrust into her opponent and inject lethal poison into them.
Dance of the Dragonfly: Compound Eye Hexagon - A six strike attack where Shinobu aims to strike and inject her target with multiple doses of poison at the targeted Demon's weak spots (such as the neck, heart, torso, etc.) in order to kill them with a large dose of poison.
Dance of the Centipede: Hundred-Legged Zigzag - An attack where Shinobu uses her full speed to run a zigzag pattern to confuse her opponent in order to create an opening for her to directly stab her opponent's neck and inject poison to kill them, with the stab's force and power being further enhanced by the momentum of her speed. Doma noted that the sheer speed of this technique is strong enough to destroy an entire wooden bridge.
Body Modification
Poisonous Body: In order to defeat the Upper Rank 2, Doma, Shinobu heavily altered her body by absorbing and altering her body's physiology with highly concentrated Wisteria-based poison over a period of a year. She is successful in saturating her body with the undetectable poison that has completely merged with her body's own cell structures, including those of her blood and internal organs—all the way down to the very tips of her fingernails. With Shinobu's overall size and body weight, her body is the equivalent of 37 kilograms worth of poison, approximately seven-hundred times more than the lethal amount needed to kill an average Demon, with the poison being strong enough to melt Doma, the Upper Rank 2, down to his very bones.