Shinobu Kocho is the current Insect Hashira who uses her own unique breathing technique called Insect Breathing. But before she became a Hashira, she was the Tsuguko of her sister and the former Flower Hashira, Kanae Kocho.It goes without saying that the late Kanae Kocho used the Flower Breathing technique very well throughout her time in the Demon Slayer Corps. Not only that, Shinobu's current Tsuguko and her adoptive sister, Kanao Tsuyuri, also use the same Flower Breathing technique. So why doesn't Shinobu use Flower Breathing techniques just like like her sisters?
Physical Limitation
The most effective way for a Demon Slayer swordsman to kill a demon is by severing their head. To do so requires swift movement and strong muscles, as it has to be done in one single motion. Unfortunately, Shinobu is fairly small with small arms, so it is physically impossible for her to behead a demon in a single strike.
Not only that, the Flower Breathing technique itself is quite a physically demanding technique. After all, it is a derivation of the Water Breathing technique, so it puts a heavy emphasis on strength, endurance, agility, and free-flowing movements, just like flower petals blowing in the wind. All of which are the things that Shinobu can't do.
Interest in Chemistry and Medicines
Other than the matters of her physical limitations, Shinobu also has a deep interest in chemistry and medicines, so it is only natural for her to want to incorporate her interest into her sword technique. And the way she decided to do that is by using poison.
As a Hashira, she provides the corps a facility to patch up every wounded Demon Slayer and help them recuperate. That is why Shinobu has such a deep and extensive knowledge of medicines and their effect on the body. She is highly familiar with human anatomy as well. All of those variables combined allow her to come up with a new demon-slaying method; the insect breathing technique.
Insect Breathing Technique
The Insect Breathing technique is a derivation of the Flower Breathing technique. It is an original technique that was developed by Shinobu as to circumvent her own physical limitations. Within the course of the main Demon Slayer series, Shinobu is the only user of this offshoot technique.
It is a technique that was specifically made to make proper use of her knowledge and preferred fighting style. Shinobu can't behead a demon with one clean-cut, so she opted for a thrusting and piercing attack instead. But since such movements won't be able to kill a demon, she added her knowledge on chemistry and medicines to coat her Nichirin Sword with Wisteria-based poison. That means even a tiny cut from her sword is enough to take a demon's life.
Shinobu doesn't have the physical strength to pull off a proper flowing attack of the Flower Breathing style, but since she is agile, she can move very fast. As a matter of fact, Doma, the second rank Kizuki demon, admits that Shinobu is the fastest Demon Slayer that he ever met. The combination of super speed and agility, pinpoint piercing attacks to vital areas, and deadly poison are the core elements of Shinobu's Insect Breathing technique.
Unique Nichirin Sword
In order to enhance her unique sword technique, Shinobu requires a special Nichirin Sword that is vastly different from other Demon Slayers' weapons in terms of shape, functionality, and how it is used. The blade of her Nichirin Sword is thick at the base, thin out along the length of the blade, and thickens again at the tip of the sword with a slight curve that makes it look like the stinger of an insect.
Shinobu's blade is coated with poison at all times. She puts the poison inside her specially-made scabbard that not only allows her to easily apply it, but also mix different poisons together in order to create various effects on her opponents.
That being said, a sword with such a specific function also comes with its own downside. The biggest one is the fact that Shinobu can't use her blade to defend herself from her enemy's attack. Not only that, her Nichirin Sword can't be used for either swinging or slashing attacks. After all, such a thin blade will easily break if it collides head-on with a much thicker blade. That is why Shinobu is the only one that can use her sword.
Adaptability and Originality Among Demon Slayers
In Demon Slayer, there are several ancient breathing techniques that have been passed down from one generation to the next, such as the Flame Breathing and the Water Breathing techniques. But that doesn't mean those are the only effective techniques that can be used to slay demons. On the contrary, every Demon Slayer is encouraged to find their own unique fighting style. Those techniques serve as the foundation upon which each swordsman can develop a way to fight that can leverage their individuality.
As a matter of fact, most of the Demon Slayers who have attained the title of Hashira, the strongest in the entire corps, use unique or offshoot breathing techniques. Other than the aforementioned Insect Breathing, there is also Love Breathing, Serpent Breathing, Mist Breathing, and Sound Breathing. This showcases the innate spirit of adaptability and originality among the Demon Slayers in their fight against Muzan and his minions.