Who is Koyuki in Demon Slayer? The woman from Akaza's past, explained

Koyuki is a pivotal character in Demon Slayer, intricately tied to the tragic backstory of the demon Akaza, formerly known as Hakuji. Once a frail and bedridden girl, Koyuki was the daughter of Keizo, a dojo master who took in Hakuji as her caretaker. Despite her illness, Koyuki's kind and gentle nature shone through, and she eventually became Hakuji's fiancée.

Her untimely death, caused by poisoning, deeply scarred Hakuji, driving him to a vengeful rampage that led to his transformation into the demon Akaza. Koyuki's spirit later plays a crucial role in Akaza's redemption during Demon Slayer's Infinity Castle arc.

Demon Slayer: All you need to know about Koyuki

Koyuki as shown in the manga (Image via Shueisha)

Koyuki was the cherished daughter of Keizo. However, her life was devastated by chronic illness, which kept her bedridden for the majority of her youth. Her mother, who was crushed by the despair of watching her child suffer, committed suicide, leaving Koyuki in the single care of her father.

Despite the struggles, Koyuki managed to keep a kind and calm disposition, feeling sincerely thankful towards those who looked after her, especially Hakuji, who would eventually become her fiancée. Koyuki's father, Keizo, a man of limited resources, worked all kinds of odd jobs to feed his daughter.

One time, he met a rather young man, Hakuji, who had been exiled from Edo and was marked as a criminal. After having a brawl, Keizo took the defeated Hakuji to his home and presented him to Koyuki as her new caretaker. Almost secretly, the two grew close, and Koyuki's life, which was just full of melancholy and sickness, began to change with Hakuji's presence.

Demon Slayer: The relationship between Koyuki and Hakuji

Koyuki meets Hakuji for the first time (Image via Shueisha)

Hakuji took his responsibility seriously, attending to Koyuki with dedication and compassion. He would often comfort her during difficult times, reassuring her that they would one day enjoy simple pleasures like watching fireworks together.

These conversations, though ordinary, held deep emotional significance for Koyuki, as they reminded her of the hope that she might one day experience life beyond her sickbed.

Despite her frailty, Koyuki's spirit was strong. However, she faced more challenges when the heir of the neighboring dojo developed feelings for her. This young man, who was both arrogant and violent, was incapable of understanding her condition.

During one of their encounters, he cruelly forced her outside while she was unwell, triggering a severe asthma attack. Terrified by her condition, he abandoned her, leaving her to suffer alone. Hakuji found her in distress and provided the care that potentially saved her life, further deepening their bond.

Koyuki dies due to poisoning (Image via Shueisha)

Miraculously, Koyuki’s health began to improve, allowing her to experience life more fully. During a local fireworks display, she reminisced with Hakuji about the time he had promised to take her to see fireworks when she was sick.

Though Hakuji had forgotten this promise, Koyuki had held onto it as a symbol of the future she had hoped for. Touched by the fact that someone believed in her survival and recovery, Koyuki asked Hakuji to be her husband, a proposal he gladly accepted.

However, the heir of the dojo became furious because of their engagement, and he had a personal grudge against Hakuji. Failing to win his strength in fighting, the heir instigated the treachery by putting poison into the water well at Keizo’s dojo. Tragically, Koyuki and her father drank the poisonous water on the same day and died, just when Koyuki began to live her life as a healthy young woman. She was a mere 16 years old.

Akaza became a demon after Koyuki's death (Image via Studio Ufotable)

The pain of losing Koyuki and her father was too much for Hakuji, which made him lose control. He went on a rampage, killing all of the people from the nearby dojo in a storm of destruction. This destruction caught the eyes of Kibutsuji Muzan, who Hakuji into a demon, who fans know today as Akaza.

Demon Slayer: Koyuki's role during the Infinity Castle arc

Akaza fights against Giyu Tomioka and Kamado Tanjiro (Image via Shueisha)

Years later, during a fierce battle between Akaza and the Demon Slayers Giyu Tomioka and Tanjiro Kamado, Koyuki’s spirit reappeared as a voice of reason. Though Akaza did not recognize her at first, she persistently pleaded with him to stop fighting, trying to remind him of the humanity he had lost. Her presence stirred long-buried memories within Akaza, causing him to recall his life as Hakuji and the love he once had for her.

As Akaza began to regain his human memories, he realized that his true desire was to die and reunite with his loved ones. He tried to destroy himself, but Muzan’s control over him prevented this.

Koyuki pleads to Akaza to stop fighting (Image via Shueisha)

However, Koyuki’s spirit intervened once more, gently holding his face and convincing him that his suffering was over. She embraced him, accepting his apology for failing to protect her. In their final moments, Koyuki welcomed Hakuji back with love, and together, their spirits disappeared in a blaze of flames, finally finding peace in the afterlife.

Final thoughts

In the Demon Slayer series, Koyuki is a key character in Akaza's tragic past representing the love and the humanity he lost after turning into a demon. Ultimately, it is her lasting influence that leads Akaza to rediscover his humanity, giving him the chance to change his ways and find peace in the afterlife.