WARNING: The following contains spoilers for Demon Slayer: Kimetsu no Yaiba #205 by Koyoharu Gotouge, John Werry and John Hunt, now available in English from Viz Media.
Demon Slayer is known for adding a sympathetic edge to several of the Demons encountered throughout the series. The most sympathetic is Akaza, the headstrong -- and just plain strong -- Upper Rank 3 Demon of Muzan Kibutsuji's forces. Akaza takes part in two of Demon Slayer's most impactful battles that resonate with two completely different emotions.
During the "Mugen Train Arc," Akaza and the Flame Hashira, Kyojuro Rengoku, come together in a devastatingly entertaining clash. The fight, which is featured in the Demon Slayer: Kimetsu no Yaiba movie, is a wondrous flash of Rengoku's Fire Breathing and Akaza's Destructive Death techniques. However, their differing perceptions of weakness and ideals highlight a significant point of contention that spans beyond this encounter.
Akaza and Rengoku's Clash
Akaza respects and recognizes strength while harboring an immense hatred towards those he perceives as weak. He tries to convince Rengoku of the benefits of becoming a Demon, but the Flame Hashira rebuffs his admiration. Rengoku disagrees with Akaza's take on a limited lifespan being humanity's weakness, saying, "Growing old and dying is what gives meaning and beauty to the fleeting span of human life."
Though Akaza ultimately kills Rengoku, Tanjiro clarifies that it is the fallen Hashira who won the fight. While Akaza fled from his weakness of the sun, Rengoku never faltered and kept everyone safe. Aside from Rengoku being an incredibly likable character, the profound impact his death has on Tanjiro only adds fuel to those who dislike Akaza. However, when Tanjiro and Akaza meet again, the Demon is forced to face his past, revealing the root of his hatred.
Tanjiro Confronts Akaza
Much later in the series, during the "Final Battle Arc," Tanjiro and Giyu Tomioka -- the Water Hashira -- come up against Akaza within the Infinity Castle. This battle pushes all three to reach new heights in their abilities. Giyu's awakening of his Demon Slayer Mark and Tanjiro's use of the Hinokami Kagura with the Transparent World technique proves enough to cut off Akaza's head. Despite this, Akaza's desire to grow stronger and his hatred of the weak, which he inexplicably associates with Tanjiro, allows his headless body to fight on.
While Akaza's body continues to attack Tanjiro and Giyu, the Demon's mind begins to flood with memories of his past and visions of loved ones he'd forgotten. As a human, Akaza was known as Hakuji and spent much of his youth turning to crime to provide for his sick father. His punishments from the magistrate's office were violent beatings and tattoos branding him a thief. Akaza's father eventually takes his own life, hoping that his son can get a fresh start.
Akaza Confronts His Past
Despite initially harboring intense resentment towards the world, Akaza meets a man named Keizo and his ailing daughter, Koyuki, who drastically changes his life for the better. Akaza spends the next three years caring for Koyuki and becoming the only student of Keizo's Soryu fighting style dojo. Akaza and Koyuki plan to wed, but things quickly take a horrifying turn when a rivaling dojo poisons Akaza's new family while he's away.
Akaza's retaliates with a bloody massacre of the rival dojo, capped off by Muzan meeting him and transforming the shattered boy into a Demon. Having forgotten his past, Akaza now slowly realizes his hatred stems from self-disgust over his failures to protect the people he's cared about, never being by their side at crucial times.
In the final moments of the fight, Tanjiro senses gratitude from Akaza as the Demon attacks himself, acknowledging his defeat. While Muzan urges on his Demon side, Akaza ultimately listens to his humanity and is met by his father, Keizo and Koyuki. While not absolving his wrongdoings, his loved ones welcome him home and appear to join him in Hell, with flames swirling around an embracing Akaza -- now Hakuji again -- and Koyuki as the Demon's body crumbles away.