You misunderstand, Tanjiro. I only despise the weak. I only spit on weaklings. Yes. Weaklings make me sick. It is the law of nature that they be weeded out.
As a demon, Akaza took the form of a tall and muscular young man with skin so fair that appears bright green-tinged white, decorated by a pattern of thick blue lines, which resemble the criminal tattoos he had as a human. Akaza had short, bright pink hair that fluffed out around his head, and inward-tilting yellow eyes with pink eyelashes and blue sclera that looked somewhat like cracked glass, the kanji for "Upper Rank Three" etched into their irises. The lines on his face curved through each of his eyes from below his ears to over his temples, another blue line running from the center of his hairline to the bridge of his nose, with two more lines running around his neck, three others branching off the lower one to his torso.
The center line ran directly down his chest to halfway down his stomach, and the other two branched off to the sides over each side of his chest to join the two other lines, this same three-line pattern there also repeating around his waist. On his arms there were lines running down the front of his shoulders that ran into to two more, which went around his biceps, before continuing to run down to his wrists, below which it could be seen that each of his fingers are also dark blue with an orange fingernail, his toes also sharing this unusual appearance.
He wore little, only sporting a short, sleeveless dark purple-pink haori that was cut off at his waist, left open to expose his chest, that was decorated by a square pattern on his back. Below this, he sported a pair of baggy white pants that he rolled to just below the knee with a blue rope belt to secure them at his waist. Akaza prefers to go barefoot, but wears a chain of large round pearls around each of his ankles.
During his human days as Hakuji, he had the same hair, just colored black rather than pink, and pale blue eyes with unusually-colored pink eyelashes. He was also very muscular as a human, and, on each of his forearms, he bore three black criminal tattoos. He also wore a dark blue-gray yukata.
Akaza is a strong, stubborn and impulsive demon who enjoys fighting, especially against strong Demon Slayers. He looked down on anybody he deemed weak, but genuinely respected those who were strong in his eyes, regardless of their race. Once he met someone he deems strong, he demanded to know their name, and would not stop until he finds out; he remembers all the names he's committed to memory as tribute to their strength.
Akaza had a deeply-rooted psychological need to become stronger, and did not get along with his fellow Upper Ranks due to him seeing them as his rivals. He is especially antagonistic towards and even appeared jealous of the two Upper Rank above him, Doma and Kokushibo, lashing out at Doma and vowing to kill Kokushibo. Even after being beaten down and beheaded during his fight against Tanjiro Kamado and Giyu Tomioka, he stubbornly held on and continued to fight despite not even knowing why he wanted more power.
As a human, Hakuji possessed the same stubborn personality with a big heart and resilience. He valued others more than his own well-being, and hated himself for having a life "full of empty words and promises." Even after becoming a demon and losing his memories of his human life, parts of Hakuji's memories influenced Akaza's decisions; he refuses to eat women, despite knowing it would make him stronger if he did so. His hatred of weak, cowardly people stemmed from a corruption of his human memories, where a rivaling dojo poisoned his dojo's well because they were never able to beat him.
Later after remembering the entirety of his past and all of his regrets as a human and demon, Akaza was shown to have openly begun hating himself and all of his shortcomings during his life where he wasn't there to save or protect everyone that he loved and cared for and later admitted that the person he really wanted to kill all along was himself.
Overall Abilities: As the holder of the 'Upper Rank Three' title, Akaza possessed a tremendous amount of power, having been able to defeat Kyojuro Rengoku, the Flame Hashira, and also several past Hashira, according to what he stated. Later, he is able to fight and overwhelm both Tanjiro and Giyu, even when they were both Hashira-level swordsman using their Demon Slayer Marks and when Tanjiro had access the "Transparent World". If not for Akaza losing his will to continue fighting, he would have certainly killed both of them. In a further testament to his might, he is capable of becoming the holder of the Upper Rank Three title and the fourth strongest demon in the series without killing or eating any women, which would've hindered his growth as a demon drastically.
Extrasensory Perception: Akaza possesses supernaturally honed sensory abilities able to sense things outside the normal range of perception. His extrasensory perception ability can physically manifest as his Technique Development, Destructive Death: Compass Needle. On top of being able to sense the auras of demons and humans, he can also tell how strong or weak an individual is just by looking at them. In addition, Akaza can also sense something he calls "Battle Spirit", the will of a person to fight as well as their murderous intent. This greatly increases his proficiency in battle, allowing him to predict where and how his opponents will attack and where their weak spots are. His senses are so powerful that it even shocked Giyu.
Immense Durability: As an Upper Rank demon, Akaza's body is phenomenally durable as he harbors an extremely high concentration of the blood of the Demon King, Muzan Kibutsuji. During his fight with Kyojuro Rengoku, the Hashira had trouble cutting various parts of his body even with his katana and incredible physical strength, showcasing Akaza's immense durability. Like all demons, Akaza's neck is much tougher compared to the rest of his body, so much so that Kyojuro only managed to cut two-thirds of his neck before the Upper Rank escaped, albeit Kyojuro was severely injured then.
Immense Speed & Reflexes: Akaza is extremely fast, as shown during his fight with Kyojuro when he moves at super fast speeds, moving so fast that even Tanjiro Kamado and Inosuke Hashibira couldn’t perceive his blinding movements, with the latter to remarking that he was in "a different dimension". This is further exemplified from the fact that he could move in bursts of speed so fast that it made it seem like he teleported, which he frequently displayed, managing to do so even for Tanjiro who can smell the future. Even Giyu Tomioka, one of the fastest Demon Slayers, was instantly matched by Akaza in speed despite him awakening the Demon Slayer Mark just moments before.
Immense Strength: Akaza possesses notably phenomenal physical strength. His incredulous strength has been showcased multiple times, most notably when he punches or kicks, which is strong enough to generate powerful shockwaves and break the ground. Akaza also easily broke Giyu's sword in half with a single side punch despite the latter swinging his blade down and destroy the head and jaw of Upper Rank 2, Doma, with his arm, and even pierce through Kyojuro's solar plexus. Combined with his Blood Demon Art, his strength is further increased, allowing him to cause craters in the ground by simply punching it. When he was a human at the age of 11, he is able to completely knock several grown men unconscious in a fight with nothing but his bare fists and legs. At the age of 18, even before he became a demon, he is easily able to decapitate, dismember and mutilate 67 armed adult kendo masters with his bare fists, to the point that even Muzan thought that it is a demon who performed these feats.
Immense Regeneration: Akaza possesses one of the most incredible regenerative abilities in the series due to assimilating a massive amount of Muzan Kibutsuji's blood. He is able to regenerate instantly from slash wounds both minor and severe caused by Tanjiro and even lost limbs inflicted by Giyu and Kyojuro with little effort. During his battle against Giyu and Tanjiro, his regeneration evolved even further as he didn't die even after having his head cut off by a Nichirin Blade and then completely regrow a new one afterwards, a feat considered impossible for demons and one only Muzan, the Demon King, had accomplished beforehand.
Indomitable Will: Akaza possesses an supernatural will and undaunted spirit. Despite being beheaded by Tanjiro's Nichirin Blade, he refused to disintegrate and die, instead forcing his headless body to keep fighting. He pushed his regeneration to evolve to the point where he could regrow his head, all because he simply refused to allow himself to lose. Even before he became a demon, he would relentlessly take blows from opponents way bigger than him and receive countless beatings all because of his goal to heal his sick father.
Tactical Intellect: Akaza is a genius among geniuses in regards to bare-fisted and hand-to-hand combat, especially ones related to martial arts. He has also displayed natural talent and aptitude in martial arts as well, like being able to beat up talented swordsmen and combatants from neighboring dojos while still in the midst of learning Keizo's Soryū Style. Even as a child, Akaza could fight based on pure instinct and tactical intuition and still win. This ability even surprised Giyu Tomioka, who stated that Akaza could instantly evolve and adapt to any attack or technique that he uses, to the point that he can predict when his opponents will strike and how to counter them with equal power.
Unlimited Stamina & Endurance: Akaza possesses absolute and infinite stamina and vitality, never tiring and always remaining in optimal physical and mental condition all the time as well as being able to endure waves of onslaught as if it were nothing. In the Mugen Train Arc, Akaza's hand got split open in half by Kyojuro Rengoku's Flame Breathing, Second Form: Rising Scorching Sun, but yet he seemed completely nonchalant about it, even proceeding to complement his katana. This was the same when Kyojuro unleashed the Flame Breathing, Ninth Form: Rengoku, this time, he had injuries on his arm, head and his upper torso. Akaza is also one of the only ones to withstand Tanjiro Kamado's headbutt without any signs of pain afterwards. Prior to being transformed into a demon, Akaza (Hakuji) demonstrated superhuman endurance at the age of 11 as he endured beatings that could make a grown man go numb (100 beatings) thus earning the title of "Demon Child."
Destructive Death: Akaza's Blood Demon Art takes the form of a martial arts style that combines shockwave-like techniques and his Soryu Style (
Master Hand-to-Hand Combatant: Akaza's most notable attribute as a human and as a demon is his extraordinary skill in unarmed combat and bare-fisted martial arts. Even before transforming into a demon, Akaza has displayed prodigious abilities and skills in hand-to-hand combat, being able to completely lay waste to several grown men at the age of 11 without any prior martial arts training, and annihilate 67 adult kendo masters with his bare fists, brutally mutilating their bodies until they were mangled piles of flesh when he was 18. After becoming a demon, his hand-to-hand combat prowess was further augmented to the point he could effectively fight at speeds faster than the eye can see while fully utilizing his bare-fisted martial arts skills for both offense and defense. Furthermore, when combined with his Blood Demon Art, his blows and strikes become even more powerful and lethal, making him unparalleled in unarmed combat.
- Soryu Style (
素流 式Soryū Shiki?): A bare-fisted martial arts style taught to him by Keizo when he lived with him and took care of Koyuki. The Soryu Style utilizes both a user's arms and legs to unleash swift and powerful strikes that target an opponent's neck and weapon. He used it to kill 67 kenjutsu masters with ease and it is the main inspiration of his Destructive Death Style used when he became Akaza.
- Bell Splitter (
鈴 割り Suzu Wari?): A technique likely created or inspired from the Soryu Style where Akaza strikes a sword from the side as it is descending to break it with ease.
Akaza has a unique technique called Technique Development (
- Compass Needle (
羅 針Rashin?): Deploying a light blue snowflake-shaped compass underneath him with numbers from 1 to 12 that can detect and track the locations of his opponents and incoming attacks through sensing a person's will to fight. This technique can also be used to enhance the accuracy of his attacks, as stated by Tanjiro Kamado when Akaza always instinctively aimed for his vital points as if his fists were magnets attracted to them. Akaza always has this technique activated when engaging in combat, making all other techniques he unleashes extremely difficult to counter and evade while making his techniques all the more lethal.
- Air Type (
空 式Kūshiki?): Akaza punches the empty air in front him, creating a powerful shockwave from the pressure of his fists and then sends it flying towards his enemies. These airborne shockwaves can be created multiple times and has been noted to travel faster than the blink of an eye.
- Disorder (
乱 式Ranshiki?): Punching in front of him, Akaza creates a barrage of chaotic ranged shockwaves capable of overwhelming Kyojuro Rengoku's Flame Breathing, Fifth Form: Flame Tiger.
- Annihilation Type (
滅 式Messhiki?): One of Akaza's most powerful techniques. Akaza lunges forward, punching with so much force it creates a shockwave that decimates the surroundings capable of going through Kyojuro Rengoku's most powerful technique: Flame Breathing: Esoteric Art, Ninth Form: Rengoku.
- Eight-Layered Demon Core (
鬼 芯 八 重 芯Kishinya Eshin?): Akaza unleashes eight powerful punches, each strike creating powerful shockwaves in a similar fashion to his Disorder technique.
- Leg Type (
脚 式Kiyakushiki?): Techniques where Akaza uses his legs as the main form of combat.
- Crown Splitter (
冠 先 割Kamuro Saki Wari?): A reverse, rising axe kick that creates a powerful shockwave that travels through the opponent. Tanjiro Kamado noted that a slight scrape from this attack caused him to bleed.
- Explosive Flurry (
流 閃 群 光Riyūsengunkō?): A flashing flurry of powerful straight kicks, each creating powerful shockwaves capable of launching even a Hashira a great distance and fast enough to evade his reflexes.
- Flying Planet Thousand Wheels (
飛遊 星 仟 輪Hiyūsei Senrin?): Akaza kicks with both legs in a flowing motion from under his opponent that slowly rises upward.
- Crown Splitter (
- Crushing Type (
砕 式Saishiki?): Techniques that solely involve attacks of brute force that pulverize the enemy.
- Final Form: Blue Silver Chaotic Afterglow (
終 式 青 銀 乱 残 光Shiyūshiki Aogin Ranzankō?): Akaza's ultimate martial arts technique. Akaza creates an omni-directional barrage of thin and sharp shockwaves that seemingly strike out of nowhere from a flurry of punches. This attack was so overwhelming it could completely negate Giyu's Water Breathing, Eleventh Form: Dead Calm.
- Akaza's alias contains the respective kanji for "luxuriant growth" (猗 a?), "cave" (窩 ka?), and "sit, cushion" (座 za?).
- Akaza was the only demon of the Twelve Kizuki who refused to eat or kill women, and was given special permission to do so.
- Akaza was one of Muzan's favorites since he was loyal and serious.
- Akaza's Technique Development ability forms the shape of a snowflake; possibly due to the influence of his fiancée (Koyuki's name contains the kanji for "snow", and she wears three snowflake-shaped hairpins).
- Many of Akaza's attacks and techniques are named after fireworks, a reference to his promise to Koyuki to see the fireworks.
- Akaza is the only member of the deceased Upper Ranks who encountered the people he knew in life while disappearing. There are two members of the Twelve Kizuki who have been shown experiencing this, the other being Rui.
- Akaza's Japanese voice actor has the role of Gaara from Naruto: Shippūden.
- Akaza is ranked 17th in the second popularity poll with 1982 votes.
- (To Kyojuro Rengoku) "Let me tell you why you can't enter the realm of the highest. Because you're a human. Because you're going to grow old. Because you're going to die. Become a demon, Kyojuro. Do that, and you can go on training for a hundred, two hundred years. You can become stronger."
- (To Kyojuro Rengoku) "There were never any Flames among all the Hashira I've killed until now. And no one ever took me up on my offer, either. Why do you think that is? As a fellow martial artist, I just don't get it. Not when only the chosen ones can become demons!... Watching the hideous decline of someone blessed with extraordinary powers... it pains me! I can't bear it! Die, Kyojuro... while you're still young and strong."
- (To Kyojuro Rengoku) "Even if you fight to death, you can't win, Kyojuro. Those impressive slashes you inflicted on me... have already healed completely. But what about you? A smashed left eye, shattered ribs and damaged internal organs... all irreparable. If you were a demon, you'd heal in the blink of an eye. Those would be mere scratches a demon. You can struggle all you want, but a human can never beat a demon."
- (To Tanjiro Kamado) "Nice movements. You've trained so hard in a short time span. Let me praise you. But man, Kyojuro did an amazing job. You were nothing but a weakling lying down on the ground that night. But my goodness! Look at you now! Your growth makes my eyes pop out. I'm feeling pure happiness. My heart's leaping. I'm glad Kyojuro died that night. He most likely wouldn't have been able to get any stronger than when I saw him then. And he had the dumb worldview about staying human."
- (To Tanjiro Kamado) "You misunderstand, Tanjiro. I only despise the weak. I only spit on weaklings. Yes. Weaklings make me sick. It is the law of nature that they be weeded out." 
- (To himself regarding Tanjiro Kamado) "I understood instinctively that I couldn't accept this person. He gives me an unpleasant feeling that gets on my nerves, as if nails were scratching metal. The dissonance makes me throw up. I'm misunderstanding something. In the beginning, I thought I was unhappy because he was weak. But it seems like this unhappiness isn't going away, despite him getting stronger. It seems that everything, from his eyes, voice, and words, scrape at my entrails from inside with a rasp."
- (To himself) "On the battlefield, you have to confront all unexpected situations even if it's your first time encountering them, and find a way to deal with them. I can do that. Or I should have been. But within the short span of this fight managed to surpass my speed after understanding something. Centuries of the best of martial arts, only to get beaten in a straight-up confrontation. Those eyes have no hatred or anger in them. There is no intent to murder or fight. The thing captured in his eyes is most likely the 'Supreme Territory' I always wanted. It has to be the 'State of Anatta'. I've always had a feeling that this state existed, but I should've reached that point by now."
- (To himself) "Are the poor not even allowed to live? Father... To Hell with this world! To Hell with every last one of them! Why do these rotten people get to live but my father had to die? He wasn't a bother. What did he have to apologize for? My father didn't do anything wrong! I could take the punishment. They could whip me savagely or break all my bones... but I could take it for even a hundred years for my father's sake![...] My father was rapidly losing weight. His ribs were beginning to show through his back. I wanted to feed him something more nutritious. I was sure I could heal him. Why did he hang himself? I would have been happy to die instead, if it were for my father's sake. For my father!!"
- (In regards to Koyuki) "I will cure you for sure. Help you. Protect. My life was worthless, filled with nothing but empty promises."
- (In regards to himself) "I became a demon, lost my memories and again began seeking strength. There was nothing left I wanted to protect. I didn't even want to continue living in a world without my family. For over a hundred years I committed pointless acts of carnage. It's a horribly sad... laughable... and ridiculous story."
- (To Koyuki) "Forgive me! Forgive me! I'm sorry I couldn't protect you! I'm sorry I wasn't with you when you needed me! I couldn't keep... a single promise!! Forgive me! Please forgive me!"
- (To his family) "I'm home, father. I'm back. Master. Koyuki. I'm home."