After the death of Tsutako, Giyu tried to tell others that she was killed by a Demon, however, he was labeled as mentally ill and was sent away to one of his relatives, a doctor. Giyu ran away during the journey there and almost died on the mountain, but he was rescued and became apprenticed under Sakonji Urokodaki.
Giyu was 13 years old when he met Sabito while training under Sakonji, and they became good friends due to their similar pasts and age. Together, they entered the Final Selection on Fujikasane Mountain. Giyu was injured after a Demon's attack and was saved by Sabito, who defeated nearly every Demon on the mountain. However, after the week went by, it was revealed to Giyu that Sabito was the only one who died during their selection. As a result of this, Giyu started developing a doubt for the authenticity of his position after becoming the Water Hashira.
While Tanjiro Kamado was struggling to fend off the attack from his Demon-turned sister, Nezuko Kamado, Giyu attacks the latter from behind, only to fail as Tanjiro moves Nezuko out of the way. Recovering quickly, the swordsman asks the boy why he protected the Demon, and he replies that the Demon is his sister. Looking at the maddened Nezuko, Giyu questions this statement before swiftly removing the girl from her brother's grip.
As Tanjiro calls out to his sister in alarm, Giyu tells him not to move, stating that it is his job to kill Demons like Nezuko. The swordsman then listens as Tanjiro attempts to defend his sister and explain their current predicament, commenting afterwards that her change in demeanor is simple to explain: any open wound bathed in Demon blood causes that person to become a Demon themselves, thus increasing their overall numbers. When the boy exclaims that his sister hasn't eaten any humans, Giyu reminds him of what had just transpired, shortly thereafter bluntly remarking that there is no way to cure a person once they are turned into a Demon, despite Tanjiro petitioning that there must be a way. As Tanjiro continues pleading for his sister to be released, Giyu brings his sword up to Nezuko's throat.
Tanjiro prostrates himself before the swordsman, begging for his sister's life. Giyu grows angry at his actions, stating that he has no authority over who lives or who dies. He continues that Tanjiro was too weak to protect his family, and all of his talk about finding a cure for his sister's condition and finding his family's killer is ridiculous. Stating that neither he or the Demon Lords would have any respect for such a miserable display, Giyu asks Tanjiro why he thought that covering his sister's body with his would be more effective instead of swinging his hatchet and that Tanjiro's mistakes are what lead to her capture and states also that Giyu could have skewered them both and have been done with it. As the boy ponders these words, Giyu silently encourages him to find the resolve necessary to accomplish all of the lofty goals he had placed upon himself. He then stabs Nezuko in the chest, causing Tanjiro to throw a stone at him in fury.
Giyu blocks the stone with the hilt of his sword, avoiding another of the projectiles as Tanjiro charges at him. Seeing the attack attempt as only a simple act of emotion, the swordsman angrily drives the hilt of his sword into his attacker's back, knocking him to the ground. Staring down at the fallen boy, Giyu wonders where his opponent's axe is. Looking up, he sees the weapon spinning towards him through the air, narrowly dodging it. He then muses over Tanjiro's clever strategy, without even realizing that the boy was empty-handed when he attacked. Deciphering Tanjiro's plan, Giyu realizes that Tanjiro likely thought to take him out with the surprise attack, even if it meant perishing as well.
Distracted, the swordsman is attacked by Nezuko, dodging backwards from her kick. Cursing himself, Giyu watches as the girl reaches for her brother, certain that she was going to devour him. To his surprise, she instead stands protectively in front of his prone body, before charging at him again in rage. Giyu recalls Tanjiro's previous assertion that Nezuko wouldn't eat humans, noting that somebody a long time ago had said the same thing and had been killed regardless. He reflects on the nature of Demons, in particular, the high amount of stamina lost during the transformation process, and what they do to alleviate the lost stamina and prevent starvation: eat humans, even those closest to them. Seeing that Nezuko was not following this example, Giyu sheathes his sword, incapacitating the unusual Demon with a barehanded blow to the neck.
While Tanjiro and Nezuko are unconscious, Giyu wraps the Demon in a clean cloth and straps a bamboo, muzzle-like tube across the girl's mouth. When Tanjiro regains his consciousness, the swordsman instructs him to visit Sakonji Urokodaki and to also to not take his sister out in the sun, before promptly leaving. He would later send a letter to Sakonji, requesting for him to train Tanjiro and explaining the boy and his sister's circumstances.
After receiving news of the many Mizunoto-ranked Demon Slayers perishing on Natagumo Mountain, Kagaya Ubuyashiki orders Hashira Giyu and Shinobu Kocho, the Insect Hashira, to assist the lower-ranked swordsmen.
Upon arriving, Giyu saves Inosuke Hashibira from the Father Spider Demon by cutting off its arm and easily beheading the Demon with Water Breathing: Fourth Form - Striking Tide. Inosuke is quickly impressed with his strength and demands him for a fight, assuming that the Father Spider Demon was a member of the Twelve Kizuki and by defeating Giyu, who defeated the Demon, he would be made a Hashira. Giyu berates him for his lack of awareness, stating the Demon wasn't one of the Twelve Kizuki and ties Inosuke up after he tries to argue.
Giyu later intervenes in the battle between Tanjiro and Lower Rank 5, Rui, saving the former from Rui’s Blood Demon Art: Murderous Eye Basket. He praises Tanjiro for holding out so long and that he would take care of the rest. Rui, expressing great annoyance over the appearance of another Demon Slayer, attempts to use Blood Demon Art: Cutting Thread Rotation on the Hashira. Giyu nullifies the attack with his own Water Breathing: Eleventh Form - Dead Calm, cutting apart all the threads. While Rui is in shock over how easily the technique cut through his threads, Giyu swiftly beheads him.
After Rui disintegrates with Tanjiro's hand on his back in sympathy, Giyu steps on his kimono remains, reminding Tanjiro that Demons mercilessly kill humans and should not be pitied. Tanjiro reassures Giyu that he will always raise his sword and defeat Demons to prevent further suffering to innocent civilians, however, he will be compassionate towards those he killed that showed regret and sorrow.
While contemplating Tanjiro’s words, Giyu sees Nezuko and suddenly realizes the siblings are the pair he saved on a mountain two years ago. While the Hashira processes the thought, Shinobu suddenly appears and tries to attack Nezuko. Giyu deflects her attack and she gracefully lands, coolly inquiring him about his intervention and stating that although he previously brushed away the thought of humans and Demons living harmoniously together, he protected a Demon, something that would make others hate him. Shinobu tells him to move aside so she can kill Nezuko, but Giyu doesn’t budge and replies that he is not hated, prompting a surprised Shinobu to apologize for her words as she did not know about Giyu’s lack of awareness about others’ opinions.
Giyu asks if Tanjiro can move and tells him to run, which the boy does while simultaneously thanking him and apologizing. After the two Hashira are alone, Shinobu warns Giyu that he is violating the Demon Slayer code of conduct.
After the siblings escape, Giyu manages to hold Shinobu under his arm and prevent her from chasing after them. Shinobu tries to make him explain his motive, but she is met with silence. After further pestering, Giyu finally speaks, reminiscing over how the event with the Kamado siblings occurred about two years ago. Shinobu interrupts, annoyed about how Giyu is presumably trying to make the story long as a form of retaliation against her telling him he was hated, provoking him. She uses his reaction as a distraction to try and stab him with a blade hidden in her footwear, but a Kasugaigarasu interrupts, relaying to the Demon Slayers that Tanjiro and Nezuko were to be brought into custody.
Giyu is later seen aloof at the Hashira meeting, where Tanjiro and Nezuko are put on trial. While Sanemi Shinazugawa torments Nezuko, he does not interfere and elects to observe from a distance instead. When Tanjiro goes to attack Sanemi, Giyu shouts for them to stop and that their master will be there soon, distracting Sanemi enough for Tanjiro to land a headbutt on him, shocking all the Hashira.
Kagaya Ubuyashiki presents himself and the Hashira bow down in respect. After greeting him, Sanemi inquires Kagaya about the circumstance with Tanjiro and Nezuko. Kagaya apologizes for not bringing the topic up earlier and states the siblings have his approval, in which a majority of the Hashira express great discontent with. Nichika Ubuyashiki is requested by her father to read former Hashira Sakonji Urokodaki’s letter, where it is stated that Tanjiro, Sakonji, and Giyu will all commit seppuku if Nezuko were to attack and/or eat a human. Tanjiro, after hearing Sakonji’s and Giyu’s sacrifice to keep his sibling alive, breaks into tears.
Sanemi, infuriated by Kagaya’s decision, tries to provoke Nezuko into attacking him and prove to his master that she will, in fact, harm humans, by stabbing her numerous times and presenting his marechi blood in front of her. As Tanjiro tries to call out to his sister, Obanai Iguro forcefully holds him down and renders him unable to move. However, Giyu intervenes and holds back Obanai, allowing Tanjiro’s call to prompt Nezuko into refusing the blood. Obanai, angry at Giyu’s interference, thrusts his hand away.
Following the events at the Swordsmith Village, Giyu attends an emergency meeting with the other Hashira and Amane Ubuyashiki, where they discuss Demon Slayer Marks. After Amane reveals the planned training for Hashira that have received the mark, Giyu decides to take his leave, much to the annoyance of Sanemi and Obanai. When Shinobu requests he at least explain, Giyu states that he is different from the other Hashira and exits, as Gyomei Himejima holds back a furious Sanemi.
After Tanjiro finishes healing, he receives a letter from Kagaya, where he is requested to talk one-on-one with Giyu and convince him to work alongside the other Hashira. The boy visits Giyu and talks to him about the training, much to the latter’s exasperation. After asking why he was mad, Giyu describes to Tanjiro that he should’ve stuck to Water Breathing and became the Water Hashira, as he himself was not worthy of holding the position.
Tanjiro hammers him with questions, asking him what his words meant, eventually wearing him out and finally making him admit that he technically never passed the Final Selection. Giyu goes on to reveal that he was in the same selection as Sabito, whom he met and befriended while under the instruction of Sakonji. He describes how Sabito had saved him early on and went on to defeat nearly every Demon on the mountain before his unfortunate death; in contrast, Giyu had not defeated a single Demon yet passed. This fact built his inferiority complex that made him feel unsuitable for a position as a Hashira, persuading him that Sabito would’ve likely received the mark rather than himself.
After hearing his story, Tanjiro relates Giyu’s experiences to his experiences with Kyojuro Rengoku: in both cases, they survived at the expense of the stronger, protective person’s death. Thinking about this, Tanjiro asks Giyu if Sabito’s expectations for Giyu living a fulfilled life were what held them together. These words shock the Hashira, reminding him of an interaction with Sabito where the latter convinces him to not die for the life his sister gave him. Giyu thinks of his deceased friend and sister, apologizing to them for his stubbornness and tells Tanjiro he would train.
Right after completing Gyomei’s training, Tanjiro makes his way over to Giyu’s house and witnesses an intense spar between Giyu and Sanemi. As the two continue using their respective Breathing Styles to fight, their wooden swords break and Sanemi eagerly proposes fist-fighting. Tanjiro intercepts them, asking Sanemi to calm down and offers to eat ohagi together, after figuring out Sanemi enjoyed the food. Out of anger, Sanemi knocks Tanjiro out and storms off.
Tanjiro wakes up a few moments later and Giyu explains to him that he and Sanemi were just training, not fighting, as Hashira also attend each others’ training sessions. After this clarification, Giyu and Tanjiro think of ideas to befriend Sanemi.
Following Oyakata's death, Giyu is seen with the other Hashira attacking Muzan Kibutsuji. He eventually enters Nakime's Infinity Castle alongside Tanjiro. The two are soon ambushed by Akaza, with Giyu quickly sent flying away by Akaza's Destructive Leg Form: Flowing Light Flash. Giyu soon returns, angry, and finally manifests a mark as he begins fighting Akaza, causing his speed to increase. Akaza immediately matches Giyu's new speed and eventually gains the upper hand, breaking Giyu's blade with a punch. As Akaza closes in for the final blow, his hand is cut off by Tanjiro mid-attack, saving Giyu. Giyu then re-engages Akaza once more, but is eventually defeated by Akaza's Final Form: Blue Silver Chaotic Afterglow, breaking through Giyu's Eleventh Form: Lull. Giyu then watches as Akaza is beheaded by Tanjiro.
After Akaza's beheaded body begins attacking Tanjiro, the injured Giyu defends Tanjiro, vowing to protect Tanjiro with his life even as he continues to take damage. After Akaza's death, Giyu falls unconscious from fatigue alongside Tanjiro.