WARNING: The following contains spoilers for the Demon Slayer: Kimetsu no Yaiba manga by Koyoharu Gotouge, available in English through Viz Media.
Breathing Styles are the signature techniques of Demon Slayer: Kimetsu no Yaiba in the fight against Muzan Kibutsuji's demons. There are five main Breathing Styles and countless variations developed by the swordsmen of the Demon Slayer Corps. The Hashira in particular tend to use personalized offshoots of the main five, but none are quite as peculiar as Shinobu Kocho's Insect-Breathing. Unlike the other Hashira whose Breathing Styles stem directly from the main five, Shinobu's Insect-Breathing is unique because it is a derivative of a derivative.
The five main Breathing Styles in Demon Slayer are Water, Flame, Wind, Stone, and Thunder. While each of these originates from Sun-Breathing, the original Breathing Style has been lost to time. Offshoot Breathing Styles are born when a Demon Slayer trains with one of the main five but tweaks its forms and techniques to better suit their own body and abilities. All Breathing Styles form a sort of family tree that can be traced back to the main five, and ultimately, Sun-Breathing. Insect-Breathing, however, is the only known Breathing Style that is two steps removed from the main five, as it comes from Flower-Breathing, which is an offshoot of Water-Breathing.
Shinobu Kocho is the creator and only user of Insect-Breathing, which she developed during her time spent as Tsuguko under the now-deceased Flower Hashira, her older sister Kanae. While Kanae's Flower-Breathing lives on thanks to Kanao Tsuyuri -- the Kocho sisters' adopted youngest sister -- Shinobu made her older sister's Breathing Style her own by using it to create Insect-Breathing. Shinobu's signature Breathing Style has four known forms; Butterfly Dance: Caprice, Dance of the Bee Sting: True Flutter, Dance of the Dragonfly: Compound Eye Hexagon, and Dance of the Centipede: Hundred-Legged Zigzag.
All Demon Slayers, even Hashira, who create derivative Styles to better suit themselves do so to maximize their skills, but Shinobu was forced to create her own Style so that she could be a Demon Slayer at all. At 4'11" and 82 lbs., Shinobu Kocho's small stature means that she does not possess the physical strength needed to decapitate a demon. For this reason, each of Insect-Breathing's forms is focused on high-speed, disorienting movements, and thrusting techniques, so that Shinobu can inject a demon with deadly poison and get back out of range of any physical attacks. A high enough dose of Wisteria poison can kill any demon, and Shinobu has become an expert in poisons so that she can kill demons despite lacking the strength to decapitate them.
As of the end of Season 2 of the anime, Shinobu has only been seen in battle once during the "Natagumo Mountain" arc where she easily defeated one of Rui's siblings. Using Insect-Breathing, Butterfly Dance: Caprice, Shinobu easily injected the demon with a lethal dose of poison before the demon even knew what hit her. Despite her petite physique and unusual Breathing Style, Shinobu Kocho is no pushover. In the manga, when Shinobu battled Doma -- Upper-Rank Two, Shinobu busted out each of her Insect-Breathing forms. Doma even commented that the speed of Shinobu's techniques would probably have beaten him if she only had the strength to decapitate him.
Shinobu Kocho isn't the force of nature that some of the other Hashira are, but she's no less worthy of her title for her inability to decapitate demons. Her creation of Insect-Breathing is the byproduct of her unyielding resolve to eradicate demons so that someday no one else will have to feel how she felt when her parents were slaughtered in front of her. She wasn't gifted with the physique of someone like Gyomei Himejima or the Hashira who saved her and Kanae in the attack that killed their parents, but Shinobu still found a way to become his equal.
