Suffering and Floundering as You Move Forward

The Spider Demon produces a pocket watch and lays out the phases of Zenitsu's transformation: tingling limbs, dizziness and nausea, sharp pain, and finally a shrinking body and lost consciousness, after which he will wake as a spider demon. Surrounded by crawling spiders, Zenitsu flees up a tree, openly admitting that running solves nothing. The demon mocks him, assuring him that once the change finishes he will lose his mind and feel nothing. Zenitsu retorts that he wants none of it and jabs that the demon surely has no friends, which leaves the creature seething.

His panic mirrors a memory of clinging to a tree during training while his master scolded him to pull himself together. Zenitsu wailed about dying, called the old man Gramps, and tearfully thanked him for clearing his debts even as he doubted he could ever become a Slayer. He described training without sleep and seeing no progress. As Gramps insisted the boy had real talent, a bolt of lightning struck Zenitsu, leaving him with his now famous blond hair.

Back in the present, clumps of Zenitsu's hair fall out, an effect the demon never mentioned. Overwhelmed by fear, Zenitsu falls asleep, baffling his opponent. While unconscious he performs Thunder Breathing's First Form, Thunderclap and Flash, springing off the trunk to attack. The demon spits poison, which Zenitsu evades midair, but he is then swarmed and harassed by acidic spit, and the demon notes he seems to know only a single form. Zenitsu recalls Gramps telling him that mastering one form was enough, comparing the refining of a sword to the beating he endured, and urging him to become a blade stronger than anyone.

Zenitsu's past as a trainee is revealed, including the lightning strike that changed his appearance and his deep bond with his master, Jigoro Kuwajima. The chapter continues the fight between Zenitsu and the Son of the Spider Family.

It is established that Zenitsu can use only the first form of Thunder Breathing, a limitation his master reframed as a path to mastery rather than a weakness.

This Mount Natagumo Arc chapter was adapted in Episode 17 of the anime. It is a defining moment for Zenitsu's character, blending his cowardice with hidden resolve.

The flashbacks introduce Gramps' philosophy that perfecting a single technique can surpass scattered mastery of many, a principle that defines Zenitsu's fighting style.