Akaza/Relationships

Father
When he was human, Hakuji loved and cared for his ailing father, but since they could not afford his medication, Hakuji had to resort to stealing in order to afford his father's treatment. When his father discovered that Hakuji had been arrested and beaten for his crimes, he felt guilty and committed suicide. In his letter to Hakuji he mentioned that he "didn't want to live on if it meant stealing from people" and he felt remorseful for troubling Hakuji to care for him.

Hakuji grew frustrated and angry after his father's death, and proceeded to violently fight throughout the town, resulting in his exile. Hakuji would take his rage out on the townspeople, trying to make sense of why his father needed to die as oppose to anyone else, showing the immense emotional pain he was in over his father's death.

Later on when Hakuji becomes engaged to Koyuki, He travels all the way back to his hometown despite being banished, and visits his father's grave to inform him of his engagement.

When Akaza remembers his father in the afterlife, he immediately asks him if he is suffering, still showing concern over his health. He falls to his knees before his father and apologizes to him for continuing his life of crime as a Demon, displaying his remorse.

Koyuki
During Hakuji's stays at the Keizo Dojo, Hakuji was usually tasked to tend Koyuki when he was not training. He used to attend her throughout the night and carry her to places she couldn't go by herself. While Koyuki was sorry for taking his time, it is noted by Hakuji himself that nursing Koyuki healed his heart. One day, Hakuji promised to watch the fireworks with Koyuki once she recovered, though he forgot about this.

During the three years they spent together, both of them eventually got close to the point that Keizo agrees to marry Koyuki with him. When they were betrothed to each other, Hakuji and Koyuki went out to see watch the fireworks, where Koyuki meekly confessed how amazing she thought he was, since he saw a future for a physically weak girl like her. Koyuki then proposed to which Hakuji tearfully accepted; promising to become stronger than anyone else and protect her for his entire life. However, their promise is short-lived, as Koyuki and Keizo were poisoned to death by the rival dojo. Koyuki's death brought immeasurable grief and rage to Hakuji, to the point where he killed all 67 members of the dojo. Koyuki's death is also what makes Hakuji, now turned into the Demon called Akaza, to hate weak people, his unwillingness to eat women, and strive to become even stronger. Although in the end, he doesn't know why.

After Tanjiro managed to decapacitate Akaza, he was about to regenerate and to strike back as ordered by Muzan. However, Koyuki spiritual apparition appeared before him and thanked him, saying that he had done enough. Akaza spirit then reverts back to Hakuji as he cries and apologizes to Koyuki as he was not strong enough to protect her at that time. Koyuki tearfully accepts Hakuji's apologies and follows him to hell as her husband, thus ceasing Akaza's will to fight and dies peacefully.

Keizo
Following the death of his father, Hakuji goes on a rampage and begins to fight with a crowd of men. As a result of the commotion, Keizo is called to settle the fight and discovers that Hakuji has knocked all of the men unconscious. He attempts to recruit Hakuji as a student at his dojo after being impressed by his fighting skills, and notices the criminal brandings on his arms. Keizo comes to understand Hakuji's situation and promises Hakuji that he will be reborn as one of his students, showing his genuine concern for his well being. He further provokes Hakuji by challenging him to a fight, but when Hakuji attempts to attack Keizo, he is swiftly knocked out by the dojo instructor.

After defeating and seeing Hakuji's potential, Keizo happily invited him to become a pupil of his dojo and instructed him to become the caretaker of his sickly daughter. For the next couple of years, Hakuji proceeded to diligently train under Keizo's instruction and soon became well loved by his teacher to the point where he offered his daughter to marry Hakuji. Keizo's warm acceptance of Hakuji brings joy to his life and he begins to see Keizo as an inspirational father figure as well as a respected teacher.

However, upon learning of Keizo's and Koyuki's murder at the hands of the rival dojo, Hakuji once again falls into a homicidal rage and proceeds to brutally murder 67 members of the dojo. Their death affect him greatly to an extent that he doesn't attempt to fight back when Muzan converts him into a demon, even saying that "I don't care anymore, I don't care about anything." Displaying his realization that he had lost the most important people in his life, yet again.

During his battle against Tanjiro as the Demon Akaza, he gets struck by the swordsman with such a strong impact that he remembers Keizo disciplining him. Then envision of his master causes Akaza to slightly regain his humanity and cease his will to fight. Keizo's spiritual apparition comes forth to remind Akaza once again that "even in death he will not forsake him" but that he must pay for the sins he has committed. Within Akaza's final moments, Keizo still guided him as a son and pupil, eventually reuniting in the afterlife.

Tanjiro Kamado
Upon first meeting Tanjiro, Akaza attempted to immediately kill him without engaging in battle, seeing him as a "weakling" not worthy of his attention. Later on, when Akaza successfully defeated Kyojuro Rengoku, he fled the scene in order to escape the sunrise, but was stabbed in the back with a blade thrown by Tanjiro. During that instance, Tanjiro began to call Akaza a coward for trying to escape while insulting Kyojuro claiming that he was the true winner of the battle.

Enraged by Tanjiro's comments, Akaza's veins can be seen visibly protruding through his skin as he solemnly specifies that he was running from the sun, not from the demon slayers. Later on, when Akaza finishes his meeting with Muzan, he angrily destroys the blade that was thrown at him into pieces. He envisions Tanjiro's face, and promises that he will "spill [his] brains" the next time they meet.

When they meet again in the Dimensional Infinity Fortress, Akaza excitedly ambushes Tanjiro and Giyu where he then proclaims that he's "surprised a weakling like [Tanjiro] is still alive." As the three of them proceed to engage in battle, Akaza expresses his delight to see that Tanjiro had improved vastly in skill and power compared to when they first met, and goes on to "praise" Kyojuro for dying in order to aid in Tanjiro's development. His comments enrage Tanjiro, who claims that he has no choice but to defeat Akaza in order to protect mankind and expresses his pity for not feeling any humane empathy.

Baffled by his words, Akaza begins to recall his memories from when he was a human and begins to remember phantom visages from his past and caused him to remember important people from his life as a human, causing severe emotional inner turmoil for the Demon, who began seeing this person's form overlapping with Tanjiro due to the young Demon Slayer's kindness reminding him of "someone". Unable to process his long-forgotten emotions, Akaza thus then decreed that Tanjiro was "unpleasant" and needed to be killed immediately causing him to completely drop whatever friendly facade he had and focus on killing him as soon as possible. However, in the end Tanjiro manages to decapitate him since Akaza could not read his battle spirit. Eventually during the course of their battle as he regrows his head, Akaza then fully remembers his life as Hakuji and all of his loved ones that he lost during this period of his life.

Even as he is decapitated and Akaza now more enraged then ever for remembering his centuries old pain and grief, forcibly regenerates his head through his determination to become stronger and Muzan's own interference of controlling him and once again mounts a attack against Tanjiro and Giyu. Refusing to give up despite losing grip on his sword, Tanjiro desperately punches the demon, once again reminding the Demon of his beloved teacher, eventually and successfully causing the demon to completely lose his will to fight on against them as he uses his own attack, Final Form: Blue Silver Chaotic After Glow on himself. Congratulating the Young Demon Slayer for making him remember his loved ones and the real reason for his desire for more power and strength. As he disintegrated to ash and is finally reunited with his loved ones in the after life, Tanjiro noted that the moment before Akaza activated his last technique on himself, Tanjiro smelled that the demon felt grateful to him and saw a slight smile on the Upper Moons face before launching his suicidal attack on himself.

Muzan Kibutsuji
Muzan first meets Hakuji after the latter finishes his massacre. Muzan was the one responsible for Hakuji to turn into Akaza.

Doma
Akaza despises Doma for a few reasons, one of them being him envying Doma as Upper Moon Two.