Tanjiro Kamado and Giyu Tomioka vs Akaza

Tanjiro Kamado and Giyu Tomioka vs Akaza was a battle that took Place in the Dimensional Infinity fortress. It focuses on the battle between Tanjiro Kamado along with the water pillar, Giyu Tomioka against Upper Demon Moon Rank 3, Akaza, the man who killed the fire pillar, Kyojuro Rengoku.

Prelude
Tanjiro and Giyu are running in the fortress, trying to find Muzan and Tamayo. They have just heard about the death of Shinobu Kocho at the hands of the upper demon moon rank 2, Douma. But suddenly, a tremor appears shaking both the demon slayers. Tanjiro recognised a familiar smell, as the roof above them broke, revealing Akaza, upper demon moon rank 3. Akaza is surprised that a 'weakling' like Tanjiro is still alive and shouts his name, with Tanjiro screaming his name in return. Thus begins the fight between the 3, a way for Tanjiro to avenge the death of the fire pillar, Rengoku Kyojuro, a man Tanjiro admired a lot, who died at the hands of the demon.

Improved Performance
As Akaza advances, Tanjiro dodges his punch and uses Dance of the Fire God : Fire Chariot on Akaza, and with considerable effort, severs the demon's arm. As Tanjiro attempts to recover, Akaza attempts to behead Tanjiro with a back-fist punch which Tanjiro dodges and counters with Dance of the Fire God : Parhelion Rainbow managing to create a long cut on Akaza's face. Looking at this fight, Giyu is quite amazed and surprised by Tanjiro's sudden and quick improvement, comparing that of a pillar. Akaza remembers Kyojuro's words about Tanjiro not being weak and accepts it as a fact and decides to show respect to him by activating his Technique Deployment indicating that the real battle has just begun.

Water and Fire
Giyu enters the fight, immediately using Breath of Water -Third Form : Dance of the Swift Current, Akaza is instantly impressed as it has been 50 years since he ran into someone this good and used Destructive Kill : War Style, a flurry of punches that produced giant shockwaves. In order to negate these shockwaves, Giyu used his own creation, Breath of Water -Eleventh Form : Lull, Akaza remarked that he had never seen it used by the previous water pillars he last fought. While Tanjiro tried attacked from behind using Dance of the Fire God: Scorching Crimson Mirror. Akaza appeared from behind and attempted a backhand chop, while Tanjiro was trying to use his technique, when Giyu cut the attacking hand with Breath of Water -Second Form : Water Wheel As Giyu was attacking the demon, Tanjiro tried to trip him by trying to use Dance of the Fire God: Flame Waltz on his legs, but was stopped and countered by Destructive Kill - Leg Form : Cap Tip Slice. Even though Tanjiro blocked it, he still spat blood. Akaza, while battling Giyu, got impressed by the pillar's swordsmanship and asked his name. Giyu refused and Akaza told that he would ask again and again and kicked him with his Destructive Kill - Leg Form : Flowing Light Flash which launched him to another side of the fortress, through various walls.

The Strong Should Aid and Protect the weak
Akaza managed to know the water pillar's name due to Tanjiro shouting his name and both attacked each other with Tanjiro using  Dance of the Fire God : Bone Burning Sun  and Akaza using Destructive Kill Dual Layered Demon Wick.

Akaza praises Tanjiro's improvement and claims that Kyojuro did an amazing job and was glad that he died, enraging Tanjiro. Akaza then gave his philosophy of how he hates the weak and wish they got eliminated. Tanjiro retorted by saying that even Akaza was once a child and someone helped him and told that the Strong should aid and protect the weak and won't let Akaza do as he like any further.

Flickering Memories
Tanjiro's words shook Akaza as he feels restless and the memories of Keizo appear telling him the same things Tanjiro told him about becoming stronger and helping people. But Akaza brushed it off and realized it was but a hallucination. Angered, he claimed Tanjiro to be unpleasant and used Destructive Kill - Crush Style : Willow of a thousand flashes and became much more faster with Tanjiro attempting to dodge. The demon surprised Tanjiro and kicked him with his Leg Style - Ring of a Thousand Flying Planets, making the young demon slayer cough up more blood. Tanjiro compares Akaza's precision to that of a Magnetic Compass and begins to think and deduce using the demon's moves and words.

He then dodges a kick by Akaza and attacks him with Dance of The Fire God : Soaring Flame Haze, but Akaza manages to dodge it, not without a considerable portion of his neck being sliced and was amazed by the technique, asking how did he swing his blade. Tanjiro attempts to use Flame Waltz but the sword was clasped in Akaza's hand, attempting to break it.

The Mark Appears
Tanjro used headbutts and kicks for Akaza to loosen his grip, but the demon won't budge. Luckily, the hands got cut by Giyu, angry about the deadly kick Akaza gave him. Giyu's senses awakened and a mark appeared on his face. He easily dodged a shockwave punch and gave a quick slice of his own. Akaza dodged but the attack slicked a small portion of his neck. The demon acknowledged the increase in speed as Giyu surprised him with a sudden Breath of Water Fourth Form : Striking Tide vertically slicing Akaza's right arm.

Tanjiro notices that Akaza has matched Giyu's speed and thinks about why Akaza's attacks are accurate and remembers words from Akaza and remembers Inosuke talking about him being able to sense killing intents and how he cannot detect people behind him if they have no killing intent.

Meanwhile Giyu and Akaza seem to be evenly matched. Tanjiro attempts to use the Flame Waltz again but was stopped by Akaza who then tries to use a Back-fist strike, which was dodged by Tanjiro. Using this opportunity, Giyu attacks the demon. Tanjiro gets a grasp about the truth behind Akaza's Techniques.

The See-Through World
As the fight between Giyu and Akaza goes on, Tanjiro remembers the time his father, Tanjuro, explain to him about correct breaths and movements and about being able to see the See-Through World one can achieve if the mind becomes invisible. He demonstrated by killing a bear while showing no killing intent. Tanjiro managed to achieve it for a short moment in time when Akaza attacked him, as he closed off other senses as he focused on dodging.

Akaza and Giyu are battling fiercely, trading blows to each other. The water pillar has used up all his forms during the fight and Akaza proclaims that it will be the end of the pillar, amazed how long he fought for. As Giyu was about to attack the demon's fist, Akaza broke Giyu's sword by punching it from the side and attempted to punch through him, but his arm was severed by Tanjiro, who was able to optimise his breaths and senses, avoiding being sensed by Akaza. The demon also noted the changes and wanted to kill the young slayer. Giyu took the moment to attack him, but Akaza used his strongest technique Technique Deployment End Style: Chaotic Blue Metal Afterglow. Giyu tried to reduce it with Lull but the attacks were so random, that he got hit by the many shockwaves, though he managed to dodge several blows.

Meanwhile Tanjiro was able to see everything move slowly in the see-through world. Akaza was unable to notice that Tanjiro was behind him, Giyu hoped he went for the neck this instant, but Tanjiro called the demon out. Akaza turned to strike, but Tanjiro dodged. Akaza could not detect his battle spirit via the compass. Tanjiro managed to decapitate Akaza with Dance of the Fire God : The Setting Sun.

“Hakuji-San, stop already!”
Akaza was bewildered, wondering how did Tanjiro not have a battle spirit and felt like he was fighting against a plant. He acknowleged that Tanjiro surpassed his speed. He then tried to attach his head back, but Giyu threw his broken sword, piercing the head, separating it from the body. His head disintegrated, but, his body continued to fight, using his Technique Deployement and set up a compass, with the head portion continuing to regenerate.

Tanjiro dodged his chops but was thrown aside by the demon's kick. Tanjiro tried to get up and fight, but the stress and exhaustion of the fight caused him to pass out. Giyuu then protected Tanjiro with his Breath of Water Fourth Form: Striking Tide, slicing the headless body in various regions, but the demon is regenerating faster. The two began to trade blows, but Giyu was badly hurt, but still decided to protect Tanjiro, giving Akaza vague memories of Keizo. As he advances, he was stopped by the teary-eyed spirit of his human self's deceased fiance, Koyuki, telling him to stop already.

Thank You
Giyu continued to stand up, despite being burdened with the desire and goal to not let his friends or family die in front of him (like his sister and Sabito). Akaza was held by Koyuki's hand as his head continues to regenerate.

He begins to remember why he wanted to become strong and remembers the time he was the "Demon Child" Hakuji from his father's death to meeting Keizo and Koyuki, finding a purpose and reason in life, finding someone to protect, then the moment it all came crashing down, his massacre of the Kenjutsu students, his encounter with Muzan and his transformation into a Demon. During this, Tanjiro manages to get up, as Akaza's head has halfway recovered. The demon attempted to kill Giyu with his Obliteration Style. Tanjiro rushed to stop him, but his sword slipped and he punched Akaza, causing him to question his current deeds and begins to regret sullying his master's precious style and prepares his Destruction Kill War Style. Tanjiro tries to pull Giyu away but, with a smile of gratitude in his face, he used the technique on himself, mutilating him and reducing many parts of his body to bones.

Akaza admits defeat, stating that Tanjiro's technique was magnificent and wants to go to hell like a man. He imagines his father and Keizo, but when he rememebers Muzan asking if he wanted to get stronger, he began to regenerate, but it was stopped by Koyuki, who was thankful about Hakuji recovering his memories and thanked him for what he has done. Finally finding peace, Akaza disintegrated, dying as Hakuji, loyal son, protective student and faithful lover.

Aftermath
Hakuji reuinted with his father, Keizo and Koyuki in hell. Tanjiro was glad that it's over and wanted to reach Tamayo, but he fainted. Giyu also lost consciousness and slumped onto his sword out of fatigue. Akaza's death was spread by a Kasugaigarasu and was heard by the other upper moons. Kokushibou lamented that he could not get any stronger and called it 'weak'. While Douma began to openly weep and mourn his 'Best Friend' (it was a facade).

Shortly after the fight against Kanao and Inosuke against Douma, Tanjiro woke up with Giyu cauterizing wounds and received knowledge of the Upper Moon 2's death.