Demon Slayer Episode 17 Rerun: Zenitsu’s Emotional Backstory with His Grandfather Sparks Tears and Thunderclap Flash Sixfold

The all-episode rebroadcast of the Demon Slayer: Kimetsu no Yaiba anime series aired its seventeenth episode, “Mastering a Single Thing,” on August 2, 2026. This episode is widely regarded as a fan-favorite, with many calling it the moment they fell in love with Zenitsu or the episode that got them hooked on the series.

Based on the manga by Gotouge Koyoharu, the anime follows Tanjiro Kamado, a boy whose family is slaughtered by demons and whose sister Nezuko is turned into a demon. He joins the Demon Slayer Corps to find a cure for her. The series has sold over 220 million copies of its compiled volumes.

Produced by ufotable, the anime began with the “Tanjiro Kamado Risshi-hen” in April 2019. The latest installment, Demon Slayer: Kimetsu no Yaiba: Infinity Castle Arc, is being released as a trilogy, with Chapter 1: “Akaza’s Return” opening in theaters on July 18, 2025.

Note: The following contains spoilers for Episode 17. Please proceed with caution if you have not seen the episode.

Turning Around to Find a Human-Faced Spider

In Episode 17, after defeating the mother spider on Mount Natagumo, Tanjiro tends to the injured Inosuke and wonders about the mountain’s strange situation—demons that should not be living in a group, and the presence of a member of the Twelve Kizuki.

Meanwhile, Zenitsu, wandering with his sparrow Chuntaro, gets pricked by something. He complains about the smell and the creepy spiders, then hears a noise behind him. Turning around, he finds a human-faced spider and screams, running away in terror. Fans online loved his panicked reaction: “Zenitsu’s scream! LOL” and “Zenitsu is so loud from the morning, hahaha (is this fan service?)”

Zenitsu Agatsuma Voiced by Hiro Shimono

Zenitsu begs for it to be a dream, hoping to wake up with Nezuko’s lap pillow. Fans commented: “He’s so honest. He complains but he’s a good guy.” and “Even in this situation, he still wants Nezuko’s lap pillow—he never changes.” Zenitsu is voiced by Hiro Shimono, known for roles like Dabi in My Hero Academia and Connie Springer in Attack on Titan.

In the official cast comment for the rebroadcast, Shimono said: “This episode shows both Zenitsu’s comedic and serious sides, and it’s an impressive episode that reveals what feelings he had when he joined the Demon Slayer Corps, despite being so scared and loud.”

Official Twitter comment

“I Want to Change. I Want to Become a Proper Person.”

Zenitsu stops running and finds people hanging from spider webs. A giant spider demon (the brother) appears and tells him he will become a spider too. A poison is spreading from the earlier prick. The brother gives him a pocket watch and says when the long hand goes around once, he’ll be a spider. Fans found the detailed explanation amusing: “A spider that explains things politely.” and “The brother spider is so meticulous.”

The brother spider is voiced by Showtaro Morikubo, known for Goro Shigeno in Major and Yusuke Makishima in Yowamushi Pedal. Fans noted: “The brother spider is creepy but has a cool voice.” and “Morikubo is perfect for this role.”

Zenitsu, crying that he doesn’t want to become like that, remembers his grandfather who took him in. The backstory reveals that Zenitsu was used by a woman for money and was in debt. His grandfather, a former Hashira, trained him. Zenitsu ran away, climbed a tree, and was struck by lightning, turning his hair from black to blond. He always felt he wasn’t good enough, but his grandfather never gave up on him. Fans were moved: “Zenitsu’s monologue here is relatable.” and “The episode with Zenitsu and his grandfather really hits hard.”

“If You Can Only Do One Thing, Master It Completely.”

As small human-faced spiders approach, Zenitsu loses consciousness. The brother spider scoffs at him. But then Zenitsu, while falling from a tree, unleashes Thunder Breathing First Form: Thunderclap and Flash. He uses it repeatedly, dodging attacks. The brother realizes Zenitsu can only use one technique. But his grandfather had told him: “You are fine as you are. If you can only do one thing, master it completely.” He explained that forging a sword removes impurities, and that’s why he hit Zenitsu every day. “You may cry, you may run away, but never give up.” Fans were in tears: “The interaction between Zenitsu and his grandfather is so emotional.” and “I cried from the morning.”

Zenitsu’s grandfather, a former Hashira, was voiced by Shigeru Chiba, known for roles like Megane in Urusei Yatsura, Rei Ichido in High School! Kimengumi, Shigeo Shiba in Patlabor, and Captain Buggy in One Piece. He commented: “Everyone has at least one thing they are good at or like. That is a small seed of talent. Zenitsu was such a child. Zenitsu, you are my pride!”

Official Twitter comment

“Thunder Breathing First Form: Thunderclap and Flash Sixfold”

Despite being poisoned, Zenitsu unleashes the Sixfold version of Thunderclap and Flash, beheading the brother spider. He remembers his grandfather’s words: “Don’t give up!” He uses breathing to slow the poison, thinking that if he runs away, his grandfather will hit him, and Tanjiro will be angry. Fans were amazed: “The Thunderclap and Flash is beautiful.” and “Sixfold! I get chills every time.”

@anime_kimetsu_official Thunder Breathing First Form: Thunderclap and Flash Sixfold | Tanjiro Kamado Risshi-hen Episode 17 “Mastering a Single Thing” | Demon Slayer: Kimetsu no Yaiba: Infinity Castle Arc Chapter 1 now in theaters since July 18! #鬼滅の刃 #DemonSlayer #無限城編 #InfinityCastle #アニメ #映画 #anime

Meanwhile, Tanjiro hears the thunder-like sound and decides to go check it out, leaving Inosuke behind despite his protests. A girl-like demon appears, followed by a giant called “Father,” who attacks Tanjiro.

Next Episode Preview

The next episode preview features “Chu-ikkan!! Kimetsu Gakuen Monogatari,” where Zenitsu as a disciplinary committee member has a morning pleasure. Fans commented on the strict Giyuu-sensei: “No mercy LOL” and “Unreasonable sensei LOL”. Episode 18, “False Bonds,” is expected to feature the appearance of a certain senior, with fans joking about “dice steak senpai.”

ufotable Twitter

Cast and Staff

Cast:

• Tanjiro Kamado: Natsuki Hanae
• Nezuko Kamado: Akari Kito
• Zenitsu Agatsuma: Hiro Shimono
• Inosuke Hashibira: Yoshitsugu Matsuoka

Staff by Arc:

Rebroadcast Information: The all-episode rebroadcast airs every Sunday from 9:30 a.m. to 10:00 a.m. on Fuji TV and other stations. Check the official website for regional schedules.

(C) Gotouge Koyoharu / Shueisha, Aniplex, ufotable