The manga series Demon Slayer: Kimetsu no Yaiba features an extensive cast of characters created by Koyoharu Gotouge.

Tanjiro Kamado (竈門 炭治郎, Kamado Tanjirō) is the eldest son of a charcoal selling family. After a demon attack kills his mother and younger siblings, and turns his sister Nezuko into a demon, he becomes a Demon Slayer to cure her. He trains in the Water Breathing (水の呼吸, Mizu no kokyū) style and later uses his family's Hinokami Kagura (ヒノカミ神楽, lit. Dance of the Fire God), a derivative of the original Sun Breathing (日の呼吸, Hi no kokyū), to create a unique and sustainable combat style. He possesses a heightened sense of smell, which aids in tracking demons and sensing emotions, and is known for his physical resilience. He initially wields a black Nichirin sword forged for him; he later uses a Sengoku period sword he finds in the Swordsmith Village.

Nezuko Kamado (竈門 禰豆子, Kamado Nezuko) is the younger sister of Tanjiro, transformed into a demon during an attack that killed the rest of their family. She retains enough memory to see humans as her kin, protecting them from other demons. Instead of consuming humans, she sustains herself by sleeping. Nezuko possesses standard demon abilities like regeneration and superhuman strength, alongside a unique Blood Demon Art (血鬼術, Kekkijutsu) called Exploding Blood (爆血, Bakketsu), creating flames harmful to demons. Her most singular trait is her eventual immunity to sunlight, which makes her the primary target for Muzan Kibutsuji. Before this, she is carried by Tanjiro in a specially designed wooden box.

Zenitsu Agatsuma (我妻 善逸, Agatsuma Zen'itsu) is a Demon Slayer who joined the Corps alongside Tanjiro. Trained in the Thunder Breathing (雷の呼吸, Kaminari no kokyū) style, he can only use the first form but has mastered it to an exceptional degree. Despite his fearful and anxious demeanor, he fights effectively when unconscious, relying on his perfected skill. He possesses extremely acute hearing, allowing him to discern people's true intentions and track demons. He wields a yellow Nichirin sword. Following the disbandment of the Demon Slayer Corps, he eventually marries Nezuko.

Inosuke Hashibira (嘴平 伊之助, Hashibira Inosuke) is a Demon Slayer raised by boars, resulting in a feral and aggressive personality. He fights using a self-taught style called Beast Breathing (獣の呼吸, Kedamono no kokyū), and wields two serrated, indigo-gray Nichirin swords. He possesses a heightened sense of touch, detecting opponents through vibrations in the air. He typically wears the head of his deceased boar mother as a mask. Despite his brutish exterior, he is a highly capable combatant. He eventually becomes a close ally to Tanjiro and his companions. Following the disbandment of the Demon Slayer Corps, he marries Aoi Kanzaki.

The Demon Slayer Corps (鬼殺隊, Kisatsutai) are an organization that has existed since ancient times and is dedicated to protect humanity from demons. There are hundreds of Demon Slayers within the organization, but they act in secrecy, even from the Japanese government. The most powerful swordsmen among the Demon Slayers are the Hashira (柱; lit. Pillars), who serve as its elite warriors.

Demons (鬼, Oni) are a race of immortal creatures that feeds on blood to survive and become stronger with each human they devour. All demons were formerly humans who lost most of their memories and traces of humanity after drinking or being injected with Muzan's blood, becoming his servants and sharing their vision and thoughts with him. Demons possess enhanced senses, regeneration, and physical abilities. Higher demons are also capable of casting powerful spells called Blood Demon Arts (血鬼術, Kekkijutsu), which are unique to each demon.

Demons are weak to sunlight, which fatally turns them into ashes upon being exposed to it. They can also be killed by decapitation with special swords used by the Demon Slayers called Nichirin Swords (日輪刀, Nichirin Tō). Demons are also vulnerable to wisteria flowers, avoiding places where they are abundant and wisteria extract being poisonous to them in sufficient doses.