Hashira

The Pillars are the top-ranked and most powerful swordsmen among the Demon Slayers in the Demon Killing Corps who serve as its elite warriors.

Overview
The Pillars are the nine most potent swordsmen among the Demon Hunters who sustain the Demon Killing Corps. Those who are of lower rank may be killed at a frightening rate, as each Pillar possesses a distinct breath style which is learned from a cultivator or developed through extreme training. The group is overseen by the leader of Demon Killing Corps Kagaya Ubuyashiki.

Pillars are continually searching for a Tsuguko (Successor), that can take their place when they die or retire. Each Pillar is assigned to a specific region that they need to protect. They also need to gather information about demons and improve their swordsmanship, because of their busy schedule, they usually would only train their Tsuguko. To become a Tsuguko, you either apply, and a Pillar accepts, or you get scouted by him. Being of the same Breath Style helps, but a Pillar still can take a successor with different Breath Style.

The time needed to become a Pillar though hard training is usually five years for ordinary people, talented and fast learners can do it in 2 years. To become a Pillar, you will also need to defeat one of the Twelve Demon Moons or 50 demons. Swordsmen who can use the breaths of flames and water have become Pillars in every era, no exceptions.

Abilities

 * Demon Slayer Marks - Pillars are the only known demon slayers (with the exception of Nezuko and Tanjiro) who are capable of displaying these marking when they are fighting demons. Out of all the Pillars, Giyu, Mitsuri, and Muichiro have successfully been able to emit these markings which are said to enhance ones physical and tactical abilities.
 * Full Focus Breathes - A tactical skill which sets Pillars apart from ordinary demon slayers. With the exception of Kanao, Tanjiro, Zenitsu and Inosuke, Pillars use this breathing method to generate an oxygen supply in their blood and strengthen their muscles. It gives them the power and stamina needed to combat demons without changing their physical form.

History
After the fight with Lower Moon One, Enmu, the Upper Moon Three, Akaza, showed up. A battle between Akaza and Kyojuro Rengoku occurred. As a result of the fight, Akaza fled, but Kyojuro died from his wounds and left an empty Pillar spot.

Not long after that, Tengen Uzui took Tanjiro Kamado and his group to a mission in the Red Light District. There, they encountered Upper Moon Six, Gyutaro & Daki. As a result of their fight, Gyutaro and Daki died, and Uzui lost his left eye and left arm, forcing him to retire and leave a second vacant Pillar spot. But despite forced retirement Tengen (along with his wives) assist with Demon Hunter Training Program.

After Kibutsuji Muzan broke into the Ubuyashiki Manor, he was attacked by Himejima Gyomei the Stone Pillar in an attempt to slay him, but Muzan escaped into the Infinity Fortress with several demon slayers chasing after them only to be separated by Nakime, the current Upper Moon Four.

Several duels broke out in the Infinity Fortress between demons and slayers. The pillars and the other demon slayers faced off against many demons who all had equal strength to a Lower Moon, Kochou Shinobu attempted to kill the Upper Moon Two, Doma, who was responsible for the death of her sister. However, she was killed and was absorbed by Doma, who is currently engaged in a battle with her apprentice, Kanao Tsuyuri. Agatsuma Zenitsu ran into the new Upper Moon Six is former apprentice brother Kaigaku, and engaged him in a duel to the death in which Kaigaku had an overwhelming advantage and nearly killed Zenitsu, but Zenitsu managed to insta-kill Kaigaku with a secret technique he created. Elsewhere, Tanjiro and Tomioka Giyu were ambushed by the Upper Moon Three, Akaza.