Back at the remains of the Ubuyashiki Mansion, Kiriya noticed that Kuina was crying. 

Kiriya: Don't cry. You must not stop drawing the outline of the Infinity Castle. We won't lose. 

Kuina: R-Right. 

Despite having to grow up fast, they were still heartbroken by the loss of their parents and their sisters. 

Outside of the building, Uzui and Shinjuro sat and listened in on everything. 

Uzui: Master Kiriya is quite amazing. He continues to intsturct the Demon Slayers despite the fact that his heart is still reeling from his father's death. He is making his own orders heard. 

Shinujuro: Yes, and I will risk my life to protect them. I will make it up to both (L/N) and Kamado for my shameful actions. Just as Kyojuro did. 

In another room... 

Nezuko was being looked after by another former Hashira. 

Sakonji Urokodaki (The previous Water Hashira and the mentor of both Tanjiro and Giyu!) 

Urokodaki: It looks like Nezuko is in pain. I did as instructed and used the medicine that you asked for Tamayo. So, can Nezuko become human again? If she does, then Muzan's goal will fall apart. His perfect dream that he sought for a thousand years to conquer the sun would go back to square one. After all these years, the only demon who did not disintegrate was Nezuko when exposed to the sun. 

He too deep breaths realizing it was the final battle. 

Urokodaki: This long fight might actually come to an end tonight. Be strong, Tanjiro. 

Back in the Infinity Castle...

(Y/N): HINOKAMI KAGURA: FIRE WHEEL! 

You dodged a punch from Akaza and went SSJ, and easily cut off the bastard's arm! 

Akaza: THAT SPEED! 

He turned to hit you, but then- 

(Y/N): HINOKAMI KAGURA: FAKE RAINBOW! 

You dodged again and then- 

(Y/N): THUNDER BREATHING: FIRST FORM: THUNDERCLAP AND FLASH: EIGHTFOLD! 

You slashed the living crap out of him! 

Tanjiro: (Y/N). This battle really means a lot to you. I can't say I blame you. You took Rengoku's death so hard. 

Giyu: (Y/N), you're so powerful. To think I would see someone going up against an Upper Moon alone, and do significant damage to them. 

Akaza: I can see you're wearing Kyojuro's haori. And is that his sword? 

(Y/N): That's right. Kyojuro is with me in this battle, and he will guide me to victory! 

Akaza: HAHAHAHAHAHAHAHAHAHA! LET THE BATTLE BEGIN! TECHNIQUE DEVELOPMENT: DESTRUCTIVE DEATH: COMPASS NEEDLE!

But then Giyu and Tanjiro tried to make a move. 

(Y/N): STAY OUT OF IT! I can handle him! 

You and Akaza went at it again as you saw an opening! 

(Y/N): GOT YOU! HINOKAMI KAGURA: FLAME WH- 

Akaza: DESTRUCTIVE DEATH: LEG TYPE: CROWN SPLITER!

He kicked you in the head, but you hardened it with Armament Haki! 

(Y/N): Yes, I'm getting used to his moves! 

Akaza: Those moves are so amazing! And that speed! THIS IS WHAT A BATTLE IS! 

(Y/N): You just love to talk don't you?! 

Akaza: YES! THAT'S RIGHT! DESTRUCTIVE DEATH: LEG TYPE: EXPLOSIVE FURY! 

He kicked at you several times, and you went flying right into a wall! 

Tajiro and Giyu: (Y/N)! 

Akaza charged in for you! 

(Y/N): FLAME BREATHING: THIRD FORM: BLAZING UNIVERSE!!! 

Akaza: DESTRUCTIVE DEATH: EIGHT-LAYERED DEMON CORE!!! 

As you slashed through Akaza, he fired eight powerful punches! 

Both of you were launched back ad landed on the ground. 

Akaza: In such a short time, you must have trained hard to match up to me. I have to admit, Kyojuro saw a lot of potential in you! I've never felt this happy before! I'm glad Kyojuro died on that night! He most likely wouldn't have been able to get any stronger than when I saw him then. And he had that dumb worldview on wanting to stay human! 

(Y/N): WHAT?! DON'T BADMOUTH KYOJURO LIKE THAT! 

Akaza: Badmouth? No, I'm not doing anything of that sort. I'm praising him. 

(Y/N): No, you're spitting on everyone's face regardless of what you say. 

Akaza: (Y/N), you just don't get it. The only people I despise are weaklings. I spit on the faces of the weak. Yes, I'm repulsed by them. The laws of nature dictate that the strong live and the weak die. 

(Y/N): No, you don't get it Akaza. The fact you're standing here now is proof. Newborn babies are weaker than everyone else. They need someone to help them live. You're the same as them. You may not remember, but you were once human. And when you were a byaby, someone protect and helped you. They're the reason you're still here. The strong aid and protect the weak! Then the weak become strong and in turn they will aid and proct those weaker than them! That is the law of nature! Akaza, I will defeat you! 

Akaza was visibly repulsed by it. 

Akaza: I thought I was enjoying myself because of (Y/N)'s massive strength. But ... those words ... when I hear them, those eyes .... when I look into them ... that voice ... when I think about it ... it ... makes me rage! 

???: In the beginning, everyone's a baby at everything they do. They get help from those around them, then remember what happened. But don't compare yourself to other people. The opponent you are fighting will always be you yourself. What's important is to become stronger than where you were yesterday. You'll become wonderful if you keep going for ten or twenty years. And next time, you'll be the one helping people. 

A man appeared behind Akaza, and he tried to strike at him, but he wasn't there anymore. 

(Y/N): What? Why did he swing at open air? 

Akaza: (Y/N), you make me sick. DESTRUCTIVE DEATH: TEN THOUSAND LEAVES FLASHING WILLOW! 

He hit the ground as you jumped! 

(Y/N): He's so fast! No ... this is more like- 

He came at you below! 

(Y/N): PRISON SHIELD! 

Akaza: DESTRUCTIVE DEATH: LEG TYPE: FLYING PLANET THOUSAND WHELS! 

He kicked you upwards, but you remained undamaged! 

(Y/N): Don't give up! I can still do this! I have to win this! I can't let Kyojuro's sacrifice be in vain! I HAVE TO WIN! Tanjiro and Giyu are here, and they're counting on me! The girls are counting on me! Zenitsu and Inosuke are counting on me! EVERYONE'S COUNTING ON ME! I WON'T LET THEM DOWN! 

https://youtu.be/zO4jWC2vTQo

Suddenly you began to transform as your eyes glowed, and then- 

(Y/N): YOU'RE GOING DOWN AKAZA! 

Akaza: Wh-What?! 

Suddenly your hair changed, it was still like a Super Saiyan's but much spikier, and your power increased tremendously! 

Akaza: What? 

(Y/N): HINOKAMI KAUGRA: SOARING FLAME HAZE! 

With intense speed, you slashed at Akaza's neck, and he noticed a massive slit and blood burst out from it! 

Akaza: This ... power ... so ... magnificent. 

At the Rengoku Residence... 

Senjuro: Bir Brother, even father has gone to where the Master is. Please, protect them all. 

Back with you... 

As you slashed at Akaza, he caught the blade, but then- 

(Y/N): GUM GUM BELL! 

You headbutted him, and then slashed his arms off! 

Tanjiro and Giyu both watched in shock at your power. 

Then flame marks appeared on you. 

Tanjiro: That's- 

Giyu: The Demon Slayer Mark! 

(Y/N): FLAME BREATHING: EIGHTH FORM: WRATH OF FIRE! 

You slashed into Akaza as his blows continued on and on again! 

Akaza: ENOUGH OF THIS! TIME TO FINISH IT! DESTRUCTIVE DEATH: FINAL FORM: BLUE SILVER CHAOTIC AFTERGLOW! 

He unleashed a final desperation attack to destroy you! 

Akaza: WHY DON'T YOU JUST BECOME A DEMON?! JUST BECOME A DEMON AND WE CAN KEEP ON- 

But then his head flew off his body! 

(Y/N): Hinokami Kagura: Setting Sun. 

Akaza: I ...lost? No! I HAVE TO GET STRONGER! I HAVE TO BE STRONGER THAN EVERYONE ELSE! 

His head disentigrated. 

(Y/N): We did it Kyojuro. We wo- 

But then Tanjiro noticed. 

Tanjiro: Akaza's body isn't even crumbling. 

Giyu: (Y/N)! LOOK OUT! 

(Y/N): WH- 

Akaza's body chopped at you, as you dodged! 

(Y/N): HE'S STILL FIGHTING?! AAAAAAAAGH! 

Akaza kicked you in the side and sent you flying into a wall! 

(Y/N): DAMN! Is this like with Gyutaro and Daki or- No, it's something else. Something is making Akaza continue fighting. 

Tanjiro and Giyu charged in and- 

Tanjiro: HINOKAMI KAGURA: CLEAR BLUE SKY! 

Giyu: WATER BREATHING: FOURTH FORM: STRIKING TIDE! 

But both of them were blown into the ceiling! 

He tried to get to him, but- 

Tanjiro: If you want to get to (Y/N)- 

Giyu: You have to deal with us first! 

Akaza then heard another voice. 

???: We are not samurai, we have no katanas. But we wield our swords in our hearts. The only thing we can use are our fists. 

Akaza tried to move, but a woman stopped him. 

???: Hakuji, just please ... stop. Just let it go. 

Akaza: Who ... are you? I ... I have to kill him. 

???: Why? 

Akaza: I have to be stronger than everyone else. 

???: Why? Why do you want to be stronger? 

Akaza began to remember his past. 

In the past... 

Akaza was a boy once named Hakuji. His father was supremely ill, and he had to steal and do everything he can to get medicine for his father. 

But then he was caught, and his father hung himself. 

He then read a note written by his father saying, "Dear Hakuji, live an honest life. You can still turn over a new leaf. I don't want to live off money that has been stolen. I'm sorry for being a nuisance." 

As Hakuji continued to fight to live, he ran into a man named Keizo, he saw potential in him. 

Keizo easily defeated Hakuji, and took him to his dojo to make him his student in the fighting style of Soryu. 

Kezio also had a beautiful daughter named Koyuki, who was ill as well. 

As time passed by, Hakuji grew close to both of them. 

And when he turned 18, Keizo asked Hakuji to take over the dojo and to take Koyuki as his wife. 

Hakuji realized it, he was happy. He finally found a place to make his life meaningful. 

But after going to pay his respects to his father, he had heard form one of the locals that a rival dojo had poisoned the well of the dojo. 

Keizo and Koyuki were both dead. Hakuji was enraged! 

He went to the rival dojo and slaughtered them all! 

In a stumble, he ran into- 

Muzan: Hmm ... I was thinking about creating 12 strong demons worthy to my cause. How about I give you some of my blood? 

Hakuji: I ... don't ... care ... anymore. 

With that, Muzan rammed his hand into Hakuji's head! 

Present... 

Akaza: Even though there wasn't a single thing left I wanted to protect. I really didn't want to live in a world where I lost my family. But for over a hundred years, I kept pointlessly murdering over and over again. I ca't go to the same place as them. 

Akaza's head then reformed. 

(Y/N): STOP! 

You ended up charging to Akaza and punching him in the face! 

But then Akaza attacked himself. 

(Y/N): WHAT?! 

Tanjiro and Giyu were jut as confused as you. 

(Y/N): Why did he- 

Akaza: No more. He beat me. Be beat me fair and square. It's over. I just want to go to hell. Dad ... are you okay now? 

Hakuji's Father: I'm fine Hakuji. 

Akaza: I'm so sorry. I couldn't fix myself. I'm useless. 

Kezio: No matter what you become, a son's a son. And a student's a student. We won't abandon you even if you die. Though ... you can't go to heaven. 

Akaza: M- 

But then Muzan grabbed him! 

Muzan: AKAZA! DIDN'T YOU WANT TO GET STROGNER?! WOULD YOU JUST LET THIS WORM BEAT YOU?! 

But then as he regenerated- 

Koyuki: Enough, Hakuji. You've done enough. 

Hakuji hugged Koyuki and cried and cried! 

Hakuji: I'M SORRY! I'M SORRY I COULDN'T PROTECT YOU! I'M SORRY FOR NOT BEING WITH YOU WHEN YOU NEEDED ME! I'M SORRY I COULDN'T KEEP ANY OF MY PROMISES! FORGIVE ME! PLEASE! 

Koyuki: I'm glad you remembered all of us. And I'm glad you returned to your old self. Welcome back, my husband. 

And then- 

(Y/N): Akaza? 

Akaza smiled at you. 

Akaza: You really ... are the best, (Y/N). 

He disentigrated as you sensed sorrow in him. 

(Y/N): (with a tear) Rest in peace, Akaza. 

Soon... 

Akaza was Hakuji again, and he saw as his father, Kezio, and Koyuki were before him. 

Back at the Infinity Castle... 

Crow: CAW CAW! CAW CAW! (Y/N) has defeated Upper Moon 3! 

Kokushibo sensed it. 

Kokushibo: Akaza, you have lost. You opened a path to further heights, and you abandoned it. You're pathetic. 

With Kanao... 

Doma: Lord Akaza has died? It felt weird for a moment just now. But it must have been just me. Oh well, it doesn't matter anyway. Because he's dead. HAHAHAHAHAHAHA! Now then, what's your name, Cutie? 

Kanao: I'm Kanao Tsuyuri, and I'm the sister of Kanae and Shinobu Kocho. 

Shinobu: (coughing up blood) Kanao. 

Doma: oh really? Well I guess all beautiful girls feel wonderful not just in taste, but also when they're inside of me. Speaking of which, Lord Akaza never ate a single woman. Even though I told him they have the best nutrients, he would get stronger from eating them, but he refused to kill them. It's unfair because that man allows him to do so in the end. Lord Muzan gave him special purposed, and yet he still died. A shame, we were thick as thieves. 

Kanao: Enough. I know that every single word you're saying is nothing but random babble. You don't feel sad about him do you? The blood hasn't drained from your face and your cheeks aren't flushed with anger. You know, Kanae actually felt sorry for you. You don't understand what happiness, sadness, or anger are. It's funny, and stupid at the same time. HAHAHAHA! Why was someone like you even born? 

Doma angrily tried to decapitate her, but Kanao slashed right into his abdomen! 

She also dodged one of his attacks with such speed! 

Doma: This girl ... can she be stronger than even the Hashira was?