The master of the Demon Slayer Corps is the head of the Ubuyashiki family, Kagaya Ubuyashiki. Ubuyashiki is the 97th member of his family that has served as the master of the corps. The Ubuyaskiki family has a curse of illness that has been passed down through the generations that weakens and drastically shortens the lifespan of every male child born. Because of this curse each male is destined to die before the age of 30. Kagaya Ubuyashiki is currently 23 and blind due to the spread of his illness.
In order to become a demon slayer, each individual must undergo the Final Selection. Final Selection takes place on Mount Fujikasane, where wisteria flowers bloom every season. Existing Demon Slayers catch, relatively weak, demons alive and place them on the mountain. Since wisteria is poisonous to demons, they are trapped on the mountain and cannot leave. Candidates will spend a week on the demon-infested mountain and if they can survive all 7 nights, they will be granted the opportunity to join the ranks of the Demon Slayer Corps.
Members of the Demon Slayer Corps are separated into ten different ranks. From lowest rank to highest, these ranks are: Mizunoto, Mizunoe, Kanoto, Kanoe, Tsuchinoto, Tsuchinoe, Hinoto, Hinoe, Kinoto, Kinoe. Once a Demon Slayer successfully passes the Final Selection and becomes an official member of the Corps, they are initially classified as Mizunoto, the lowest rank within the organization. By undertaking various missions and proving their skills and dedication, they can ascend the ranks and ultimately rise to the highest Demon Slayer position, known as Kinoe.
During the onboarding following the Final Selection, each swordsman has their rank inscribed on Mount Fujikasane. The engraving takes place through a technology called "Wisteria Engraving" and may cause an itchy or tickling sensation on the swordsman's hand. As the swordsman progresses in their Demon Slayer career, they have a means to check their current rank. By uttering a password and clenching their fist, the symbol of their rank will swell up on the back of their hand as the muscles expand. For the Hashira, instead of the rank symbol, their distinguished title is revealed, reflecting their elevated status within the Corps.
Each member of the Demon Slayer Corps gets their own nichirn sword. These swords are how the demons are killed, as the only ways for them to die are by sunlight or decapitation by a nichirin sword. Nichirin swords are made in the Swordsmith Village; a hidden village that only the swordsmiths know the location of. In order for Demon Slayers to get to the Swordsmith Village they must travel blindfolded, with their ears and noses plugged, while on the back of a Kakushi (people who work as attendants to the Demon Slayers). Even the Kakushi do not know the exact location as they periodically pass off the Demon Slayers to one another in various locations and are led by crows that are also switched constantly.
Nichirin swords (among other Nichirin bladed weapons) are the main weapons used by Demon Slayers in order to kill demons. They are forged with scarlet crimson iron sand and scarlet ore, both of which are found on high mountains like the Sunlight Mountain which is perpetually bathed in sunlight all throughout the year. Because these swords are forged with materials that have absorbed sunlight, decapitating demons with them can permanently kill them.
Nichirin swords are also known as Color Changing Katanas because they take on a distinct color when first drawn by its owner. Recruits choose their own ore for their sword after successfully passing Final Selection. Once completed the swordsmith will personally bring the sword to the Demon Slayer. After a member reaches the rank of Hashira, their weapons will be engraved with the words “Destroyer of Demons".
Each time a demon devours a human it becomes stronger and they can eventually become powerful enough to develop unique supernatural abilities known as Blood Demon Art. Blood Demon Art is different from demon to demon and most are based on a demon’s past, personality, ideals, interests, and/or occupation. Blood Demon Art may not have a singular use, and instead grant multiple abilities under the same concept or theme.
All demons possess the ability of regeneration. A demon’s regeneration usually activates immediately after any sort of damage is inflicted and can take anywhere from a handful of seconds to just mere moments to completely recover. Stronger demons, like the members of Muzan Kibutsiju’s Twelve Kizuki, have overall more powerful regenerative abilities. As demons become more powerful, their regeneration speed increases proportionally. Muzan himself can regenerate as he is getting injured, giving the perception that he’s not injured in the first place.