Zenitsu Agatsuma

A swordsman from the Demon Slayer Corps, belonging to the same cohort as Tanjirou. He is 16 years old, 164.5 cm tall, and weighs 58 kg. He is a very cowardly, passive, and selfish young man with a tendency to think negatively.

He is characterized by his golden (yellow) hair and thick eyebrows. He wears a haori with a scale pattern over his uniform. His Nichirin Sword has a blade pattern resembling lightning, with a four-lobe mokko-style tsuba, and the scabbard is primarily white. Uniquely, he has "Chuntaro the Kasugai Sparrow" instead of a Kasugai Crow. Despite being recognized for his talent by his master and possessing corresponding skills, he is bound by an inferiority complex, believing he cannot be strong, which makes him emotionally unstable. He has a very strong obsession with women, often displaying expressive faces and confusing lines. He is in love with Nezuko.

He defeats demons using "Thunder Breathing." Among the six forms of Thunder Breathing, he has only mastered the "First Form: Thunderclap and Flash," but he has honed it to the speed likened to lightning. Initially, he is weak under pressure, and extreme tension or fear causes him to faint and fall asleep, which puts him in a semi-awake state, freeing him from tension and allowing him to demonstrate his true strength. Throughout the series, he gains combat experience and trains with the Hashira, growing in skill and judgment, and during the battle in the Infinity Castle, he defeats his senior turned demon, Gyuutarou, while fully conscious.

He has exceptional hearing, which allows him to read others' emotions. He tends to believe what he wants to believe, leading him to be deceived multiple times. He was rescued from debt caused by being deceived by a woman by his later master, Kuwajima, who trained him as a swordsman. His hair turned from black to blonde after being struck by lightning during training. He reunites with his peer Tanjirou sometime after passing the final selection and thereafter joins him.

His lamentation over his own weakness is the flip side of his desire to be useful to someone. As mentioned, he does not use his negative feelings towards demons as motivation. He does not run away leaving children behind even when chased by demons, and when Nezuko's box was about to be cut by Inosuke, he resolutely confronted him, knowing from the start that Tanjirou was traveling with Nezuko, a demon, and protected the box with his life, trusting Tanjirou, who he says makes a "cry-worthy gentle sound."

He participates in the Spider Mountain Arc, the Infinity Train Arc, and the Entertainment District Arc. In the Infinity Castle, he battles his demonized senior, Gyuutarou, and defeats him with a new technique, "Seventh Form: Fire Thunder God." He also takes part in the battle against Muzan, surviving until the end. After the war, he moves to Tanjirou's family home with Tanjirou and others, and ends up marrying Nezuko.

Thunder Breathing

First Form: Thunderclap and Flash

A lightning-fast Iai slash from a stepping strike. It involves a straightforward rush, which is its limitation. Zenitsu can only use Thunderclap and Flash, but he has developed variations like the six-fold and eight-fold consecutive techniques, and a twice-usable enhanced version called "God Speed."

Seventh Form: Fire Thunder God

A new technique uniquely developed by Zenitsu. It produces a dragon-shaped lightning slash with a speed comparable to his haori-tearing "God Speed." He used this technique to defeat his fated adversary, Gyuutarou.