All the hashiras and master and his family started to contemplate the words that I have spoken and started to digest the meaning and came to the conclusion, "We have to become strong."
"Now how to become strong? I already developed a medicine to show how it works. A demo is necessary, so all of you move to combat ground. I will demonstrate the medicine usage." From my words, they became a little energized and followed me to the combat area.
After moving to the combat ground, I asked all the hashiras to attack simultaneously, which caused the hashiras to have doubts about the authenacity of my medicine and me, but I informed them and warned them to go all out with intent to kill; otherwise, they will fail. which caused them to become serious and started to attack.
For one hour, I defended against all the hashiras, which made them serious, and started to attack with intent to kill. Even then, I was full of confidence and my defense didn't vary, and I was reaching near the ideal state for my mark to appear, so I ordered them to attack all at once. They obligied and defended each and every attack, and I retaliated, causing them to retreat. I knew how to reach the ideal state and reach the mark, but I couldn't reach the mark because I didn't have my own breathing technique; that was what I needed for my mark to appear.
All the hashiras look with awe and shocked expression. How can a human who is able to defend against all their attacks and retaliate? This made them believe my medicine quality and started to bombard me with questions.
Master, who listens to battle, come to my aid. "Raja, what kind of heavenly medicine is it and what are its side effects?"
MC "The medicine name is NZT. A normal human can use 5% of the human brain, but if a person uses NZT, it increases his brain usage capacity to 50%, which makes him super genius for two hours, and side effects are that after the time duration, you will be in extreme sugglishness and hungry. You need 10 hours of sleep and need 5 people's food for consumption."
Master "excellent It is indeed heavenly medicine, which will definitely improve the combat performance of the hashiras with low side effects. With this medicine, we can fight muzan extremly well."
MC "I can't share the formula, but I will provide the medicine to Hashiras and make them improve their combat performance and help them achieve their mark, and I am trying to improve the medicine performance duration to 10 hr so we can tap muzan until morning."
Master, "Good, good. Tell me, Raja, what do you want in compensation for providing with this heavenly medicine? The Ubuyashiki family will be in your debt."
MC "I need to create my own breathing style; for that, I need to practice all types of breathing that are available, so I need your permission to learn every breathing technique from every hashira."
Master, "I don't have any problem with it, but these breathing methods are of hashiras; if you want to learn, you have to ask them."
All the hashiras expressed their willingness to show their breathing methods and swordplay.
From that day on, I trained in different breathing methods for one month straight and learned all the breathing methods. The hashiras adjusted to the medicines, and nearing their marks, all they need is a life-and-death battle. They will realize their slayer marks and grow strong once again.
In the early morning, the trio are awoken by Tanjiro's Kasugai Crow, who gives them information about their new mission. The casualties of the Mugen train are increasing, with 40 now missing; they must join Kyojuro Rengoku on-site and travel west. At noon, Kagaya Ubuyashiki speaks to Shinobu about his decision to send Tanjiro and his companions to the Mugen train mission, which she recommended he do. When asked why she thinks so, Shinobu states that it is because of his pure soul and ability to strive hard on a daily basis, adding that he managed to exceed her expectations. Above all, he has one clear goal: to defeat Muzan Kibutsuji.
Kagaya concurs with her thinking and logic. Shinobu also mentions that his father had used a "fire breathing" style, surprising Kagaya, and though he still has much ahead of him, Tanjiro could possibly be guided by Kyojuro. Kagaya comments on Tanjiro's sister becoming a demon and his encounters with Muzan, believing it may very well be his destiny to defeat him.
Outside, Tanjiro tells Aoi about his upcoming mission. She states that while they weren't together for long, she is glad to have spent that time with him and bids him good luck. He thanks her for looking out for them while being busy and hopes that through her, they can go back out to battle once again. Aoi brushes aside his gratitude, claiming it was because of luck that she survived Final Selection and ended up too afraid to go into battle.
As she laments her inability to fight, Tanjiro tells Aoi it doesn't matter; since she helped him, she is now part of him, and he can take her emotions to the battlefield, surprising her. Tanjiro leaves her by asking that she look after him should he be injured again, as Aoi stands still, awestruck by his sincerity and kindness.
In a final test, Kiyo, Sumi, and Naho, the trio, attempt to break the largest gourd. Cheered on by the girls, they all successfully break them, signifying their mastery of Total Concentration, Constant. As the girls see them off, Tanjiro suddenly sees Giyu Tomioka in the distance, calling out to him. Giyu sees they are about to embark on a mission, and he commends them for mastering Total Concentration, Constant. Tanjiro thanked him for his dedication to helping Nezuko, unaware that he was putting his life on the line for her. Unsure of how to thank him, Giyu tells him he can do so by killing demons.
Tanjiro suddenly hears the girls crying as they are about to leave and tells them to take care. Zenitsu tears up, while Inosuke is giddy over holding the food. Kiyo tells Zenitsu to learn to respect and be considerate of girls, shocking him with her blunt request. He asks whether they feel sad that he is leaving, to which the girls say they don't, disappointing him. With this, Tanjiro takes the lead, and the trio leaves for their mission.
At a train station, they see the location of their mission: the Mugen train. Inosuke is in awe at the sight of the "creature," believing it is the "master of this land." Zenitsu corrects him and states that it is simply a train. Inosuke decides to lead the charge and prepares to draw his blades, but Tanjiro stops him, only to erroneously think the train is, in fact, the "guardian spirit of the land" and that he shouldn't attack it. An annoyed Zenitsu tells him it is a train to transport people, calling him a "country bumpkin.
In front of all, Inosuke headbutts the train's carriage to attack it, causing police to arrive at the scene. They see the trio have swords and attempt to arrest them. After evading the authorities, Zenitsu explains that the Japanese government doesn't recognize the Demon Slayer Corps, which is why they can't have their weapons exposed in public. Tanjiro is dismayed to learn that all their work goes unknown, to which Zenitsu also agrees. They decide to hide the swords behind their backs, which does not work on the shirtless Inosuke.
At that moment, the train begins to move, forcing the trio to chase it and climb aboard; Zenitsu lags behind, causing his friends to help him get on. As Inosuke becomes amazed at the train's speed, Zenitsu asks Tanjiro whether it is wise to take Nezuko with him, believing the Corps' headquarters is the safest place. He reassures him of Nezuko's safety: "Wherever we go, Nezuko and I will be together. We're never going to be apart again," before reminiscing on the long journey they had taken together to reach this point. Onboard the train with them are the Flame Hashira and Lower Rank One of the Twelve Kizuki.
At the end of the carriage, there is a boy and an eagle sleeping without anyone knowing.