Zenitsu Agatsuma/Relationships

Tanjiro Kamado
Zenitsu depends on Tanjiro quite frequently during intense situations early on, such as when they come into contact with Demons. This was due to Zenitsu's low confidence in himself and a self-deprecating belief that he was a weakling. Zenitsu respects and admires his leadership but also ridicules him out of jealousy whenever Tanjiro mentions his encounters with females without Zenitsu. He also frequently gets frustrated by Tanjiro's bravery and heroism, seeing it as unnecessarily suicidal and getting dragged into dangerous situations because of it. Nevertheless, Zenitsu greatly values their friendship, due to Tanjiro's immense kindness and patience. He's quite possibly Zenitsu's first legitimate friend in his entire life. They cooperate well during battles.

Nezuko Kamado
Despite having an intense fear of Demons, Zenitsu develops a crush on Nezuko. He tries to convince her to marry him several times and never fails to mention his admiration for her whenever he sees her.

However, later down the line, Zenitsu eventually calms down around Nezuko and becomes slightly less aggressive. He often tells her stories about the rehabilitation training session which he does with Tanjiro and she missed out on, how Tanjiro cheers Zenitsu on during said rehabilitation training, and he promises at one point to take her to a flower field.

Zenitsu also protects Nezuko multiple times when she is in danger, evident during Zenitsu's first meeting with Inosuke Hashibira and the battle against Enmu in the train.

Eventually Zenitsu and Nezuko would marry and start a family as evidenced by their descendants.

Kaigaku
Both Zenitsu and Kaigaku trained under Jigoro Kuwajima as successors to the Breath of Thunder. Regardless of the shared animosity between them, Zenitsu holds a great deal of respect towards him, going so far as to punch other members of the Demon Slayer Corps that talked badly about him behind his back. Kaigaku, on the other hand, always belittled Zenitsu and called him "dirt" due to his lack of strength.

During the Hashira training, Zenitsu gives off a different, more serious vibe as if he is focused on something important. When going up against Kaigaku, Zenitsu is stern, he constantly insults Kaigaku, and is described as suddenly becoming a different person by Kaigaku himself. Despite how Zenitsu acts towards Kaigaku, in the past he had always respected him even if he hated him. Zenitsu is able to admit that Kaigaku was special and important to him, just like his Gramps. At the end of the battle, as Zenitsu falls he says he wished to use his own technique, Honoikazuchi Nokami, beside Kaigaku in battle on day, together.

Following the fight, when Zenitsu sees Jigoro, his own Gramps before him, he can't help but cry and apologize for not getting along with Kaigaku. Zenitsu thought that if he hadn't existed, Kaigaku wouldn't have became a demon and instead he would become something different. Zenitsu felt like Jigoro deserved to be paid back for helping him, so he apologizes for not being able to pay him back.

Jigoro Kuwajima
Jigoro first met Zenitsu when he saved him from a financial dilemma, taking it upon himself to train the young boy to become a swordsman and receiving a lot of respect and appreciation from the latter as a result. Under Jigoro's mentorship, Zenitsu learned the Breath of Thunder alongside another student, Kaigaku. Jigoro was strict to Zenitsu due to his inexperience, but he nevertheless continued teaching him without giving up. When it is later revealed to Zenitsu that his master committed seppuku alone after Kaigaku willingly allowed himself to be transformed into a Demon, he becomes both shocked and enraged towards the latter, feeling immense grief and pain over his father figure's departure. However, his passing causes Zenitsu to immediately focus on his training in order to personally lay his mentor's regret to rest by becoming strong enough to kill Kaigaku and redeem Jigoro's name.

Inosuke Hashibira
Zenitsu and Inosuke usually do not get along despite being on the same team, mainly due to their extremely low opinions of each other and their wildly contrasting personalities. Inosuke sees Zenitsu as annoying, loud, weak (initially), and a crybaby; while Zenitsu sees Inosuke as a violent moron who's only interested in fighting. However, in dire situations, they can cooperate well. Inosuke shows a level of admiration for Zenitsu's abilities while asleep, saying he should sleep forever after seeing how cool he fights for the first time.

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