◆ Role in the Story (Spoiler Warning)

※The following contains major plot details from the anime and film adaptations of Demon Slayer: Kimetsu no Yaiba. Proceed with caution if you haven’t watched them yet.





First Battle at the Drum House
Zenitsu's initial combat appearance comes during the mission at the Drum House (also called Tsuzumi Mansion), where his true abilities are first revealed. Initially terrified and attempting to flee from danger, Zenitsu is cornered by a demon with the ability to control the mansion's layout.

When faced with extreme fear, Zenitsu falls unconscious and enters his "sleep-fighting" state—a phenomenon where his subconscious, highly-trained reflexes take over. In this state, his timid personality disappears entirely, replaced by cold precision and extraordinary focus. His eyes close, his stance changes, and his movements become controlled and deliberate.

Despite having mastered only one technique—Thunder Breathing, First Form: Thunderclap and Flash—he executes it with perfect precision, moving so quickly that his opponent can barely react. In this battle, Zenitsu demonstrates his exceptional hearing ability, pinpointing the tongue demon's location and determining its nature through sound alone.

This battle marks Zenitsu's first demon kill and establishes his unique fighting pattern: appearing cowardly and ineffective when conscious, but transforming into a formidable warrior when unconscious. It's also the first time Tanjiro witnesses this dual nature, marking the beginning of his deeper understanding of Zenitsu's true potential.

Battle on Mt. Natagumo
During the mission on Mt. Natagumo against Rui's spider demon family, Zenitsu faces a manipulated Demon Slayer who had been turned into a puppet. While initially terrified and crying, when the puppet Demon Slayer threatens the box containing Nezuko (whom Zenitsu had already sworn to protect despite having never seen her), he shows a moment of conscious bravery.

Though he doesn't fully enter his sleep-fighting state in this battle, Zenitsu demonstrates his growing willpower by standing his ground to protect Nezuko's box even while conscious and afraid. This highlights his developing character—showing that his determination can occasionally overcome his fear even without falling unconscious.

Later in the arc, after being severely poisoned by spider venom, he continues to protect Nezuko's box while delirious and in extreme pain, further cementing his dedication to protecting those he cares about.

Source : DemonSlayer Official