The Hashira are the nine strongest and most skilled combatants in the entirety of the Demon Slayer Corps, and they are regarded as the most potent swordsmen among all the Demon Slayers.
The Hashira, in accordance with their great strength, are the most highly ranked among Demon Slayers, second only to the Corps leader, Kagaya Ubuyashiki, and later, Kiriya Ubuyashiki. As such, they are the organization's top-ranking, most elite soldiers who each serve a pivotal role in their war against Muzan Kibutsuji.

The Demon Slayer Corps is an organization that has existed since ancient times, dedicating its existence to protecting humanity from Demons.
All of the Hashira and some of the lower-ranked slayers have enhanced strength, speed, stamina, agility, mobility of the joints, and resistance to injury; all at superhuman levels. Abilities specific to certain individuals include unconscious combat, omnipresent rage, unique muscle composition, enhanced senses, and extrasensory perception.

Muzan Kibutsuji is a Demon, the first of his kind, and is the progenitor of many other Demons. He is also the Demon responsible for slaughtering the majority of the Kamado family and transforming Nezuko into a Demon.
As the first Demon to exist and as the progenitor of all Demons, Muzan is the strongest Demon in existence and possesses tremendous strength. He also has the ability to change his appearance and form.

The Twelve Kizuki, also known as the Twelve Moon Demons, is a group of twelve very powerful Demons who are under the direct command of the Demon Lord, Muzan Kibutsuji.
Each member of the Kizuki has received a larger portion of Kibutsuji's blood than other Demons, greatly augmenting their powers.

The common Demons are a race of monstrous, immortal and malevolent beings
Most Demons possess a murderous instinct to kill and devour humans, and have lost most of their memories from their human life. Demons however do still retain their original personality, except it often turns into a twisted, dark version of what it used to be.