Zenitsu Agatsuma, a Demon Slayer defined by paralyzing cowardice and anxiety, carries scars from a childhood marred by poverty, abandonment, and existential dread. Orphaned early and betrayed by a debt-ensnaring benefactor, he was salvaged by Jigoro Kuwajima, a retired Thunder Hashira, who drilled him in Thunder Breathing. A lightning strike during training bleached his hair gold and amplified his terrors, yet he persevered alongside Kaigaku, a bitter senior. Zenitsu’s combat prowess hinges on singular mastery of Thunder Breathing’s First Form: Thunderclap and Flash, honed into lethal iterations like Sixfold and Godspeed. Though he never progressed beyond this technique, his execution eclipses all peers—especially when fear renders him unconscious, unlocking preternatural speed, surgical precision, and tactical genius. These trance-like states enabled triumphs over the Tongue Demon, Spider Family heir, and Upper Six Daki. His hypersensitive hearing deciphers emotions, lies, and danger through sound vibrations, granting battlefield foresight. A paradox of trembling insecurity and unflinching loyalty, Zenitsu oscillates between panic-driven escapes and obsessive marriage proposals to evade solitude. Yet he repeatedly risks his life for others: shielding Nezuko’s box from Inosuke’s assault despite grievous wounds, battling Upper Ranks Kaigaku and Muzan, and channeling unrequited love for Nezuko into valor. His rivalry with Tanjiro Kamado mellows into mutual respect, anchoring his growth. Zenitsu’s evolution peaks during the Infinity Castle arc, confronting demonized Kaigaku. Harnessing lifelong inferiority and fury over Jigoro’s death, he consciously wields combat mastery for the first time, unveiling his self-forged Seventh Form: Honoikazuchi no Kami. Against Muzan, he fights through ruinous injuries with tempered resolve. Post-war, Zenitsu marries Nezuko, raises descendants, and embraces a stockier adulthood starkly opposed to his youthful self-image. His trajectory shifts from survivalist fear to steadfast heroism, driven by loyalty to allies and reverence for his mentor’s teachings.