Jigoro Kuwajima

Jigoro Kuwajima is the man who trained Zenitsu Agatsuma and Kaigaku. He was formerly the Thunder Hashira in the Demon Slayer Corps.

Appearance
Jigoro was a short, elderly man with visible forehead wrinkles and large, slanted eyes, as well as a straight scar with even six prongs running along his right cheekbone. He had notably bushy eyebrows and a large moustache, as well as slick white hair that he wore smoothed down to puff out around the base of his head, with what would've been a fringe also swept back away from his face. Jigoro was also missing his right leg, with a wooden peg taking its place, this feature made more prominent in the anime than the manga.

Jigoro wore a jinbei kimono like the one worn by Sakonji Urokodaki, only with a yellow-brown base color and a pale triangle pattern in the stead of the blue and water-patterned theme Sakonji sports. He also carried a thick wooden cane with him to support his body due to age and his missing leg.

Personality
Jigoro had a steadfast devotion to his students and strict training. Despite his status as a strong mentor and experience as a previous Hashira, he had a soft spot and unwavering dedication towards raising the next generation of students. Due to this passionate devotion, he was filled with grief after discovering that his former pupil, Kaigaku, betrayed the Demon Slayer Corps and joined the ranks of the Twelve Kizuki.

Zenitsu Agatsuma noted that, despite how often he whined and ran away, Jigoro never gave up on him once. He had saved Zenitsu from a lifetime of debt and taken him on as a student, and, showing unyielding patience, was happy just to see Zenitsu master the first form of his breathing technique. He had a great belief in training skills to perfect through repetition comparing it to forging and purifying the steel of their swords. This strong fatherly love for his students is further shown when he shown to be both flattered and touched by Zenitsu's declaration of his love and gratefulness for all of his efforts put into forcing Zenitsu to improve himself despite everyone else abandoning him and deeming him worthless.

History
Jigoro was the instructor of Zenitsu and Kaigaku as the former Thunder Hashira. Kaigaku managed to master all of the Thunder Breathing Forms except for the first Form, meanwhile Zenitsu had only managed to master the first Form and none of the others due to his inexperience.

He committed seppuku when his former protégé Kaigaku defected to gain the powers of a demon, According to Zenitsu, his death proved to be slow and agonizing since no one could cut off his head while he bled out.

Mount Natagumo Arc
Jigoro debuted prominently through Zenitsu's flashbacks as he was fighting the Son Spider Demon.

Infinity Castle Arc
After Zenitsu managed to kill Kaigaku, Zenitsu and Jigoro briefly meet in the afterlife. His student apologized for not being able to get along with Kaigaku. Before Zenitsu forcefully returned to the land of living, Jigoro declared that Zenitsu was his pride and joy with tears in his eyes.

Overall Abilities
As a former Hashira of the Demon Slayer Corps, Jigoro is known to have been a very powerful and talented swordsman. His combat style was Thunder Breathing, which he was well-versed in. Throughout his active time in the organization, he faced various demons. After losing his leg in battle, he decided to abandon his position as a pillar.

Breathing Style
Thunder Breathing (の): Jigoro is the primary instructor of this Breathing Style.

Trivia

 * Jigoro's title as a Hashira was revealed to be unique, as he was not called the Thunder Hashira, instead bearing the name of the "Roaring Hashira." This title was derived from the Izumi old word for "thunder" (神鳴), as in "God's Roaring", rather than the modern radical for "thunder" (雷), which is used to write the current Thunder Breathing and its styles.
 * Jigoro lost his right leg from the knee down in the middle of a battle when he was 35 years old, which is also the reason why he retired from being a Hashira.
 * His given name contains the Go-on pronunciation for "mercy, benevolent" (慈 ji), the Kan-on reading for "enlightenment, realize" (悟 go), and the common male suffix of "male child, son" (郎 ro). Meanwhile, his surname contains the Kun reading for "mulberry" (桑 kuwa) and "island" (島 shima/jima).

Quotes

 * (About Zenitsu Agatsuma) "That idiot disciple. I already said that you have talent that won’t lose to anyone, why won’t you understand—"
 * (To Zenitsu Agatsuma) "Compassion can make a person's heart infinitely tough. A sword that you swing for the sake of others can have power that is immense. You must become that kind of person."
 * (To Zenitsu Agatsuma) "Zenitsu, perfect it! It's alright to cry or go off by yourself. Just don't ever give up. Believe in yourself. You endured all that hellish training. You'll be rewarded for that without question. Work to forge yourself like a tempered blade... and become the most resilient of all! Focus on what you do best!"
 * (To Zenitsu Agatsuma) "Zenitsu, you are my pride and joy."

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Jigoro Kuwajima Джигоро Куваджима Jigorou Kuwajima Jigoro Kuwajima Kuwajima Jigoro 桑島慈悟郎 桑島慈悟郎