Tanjiro, Zenitsu, and Inosuke, who had been carried in by Demon Slayer Corps members, were laid side by side in the Butterfly Mansion's infirmary.
The interior of the mansion was filled with the smell of disinfectant, a faint aroma of medicinal herbs, and the busy sounds of footsteps.
"Hurry up! We have three critically injured patients!"
Kanzaki Aoi, the caretaker and nurse of the Butterfly Mansion, issued instructions in a clear, ringing voice.
Under her command, the mansion's children—Sumi, Kiyo, and Naho—moved busily, carrying bandages and water buckets.
They were children Kanao had taken in during Demon Slayer Corps activities, now serving as nurses at the Butterfly Mansion.
"My, they've taken quite a beating."
Ushiwakamaru looked down at Tanjiro and his companions with apparent interest.
"Ushiwaka-san! Don't just stand there, come help!"
At Aoi's urgent cry, Ushiwakamaru shrugged her shoulders lightly.
"Alright."
Ushiwakamaru swiftly fixed Zenitsu's broken ribs with a pressure bandage. Her hands were faster and more precise than those of a professional medic.
"Aaaah! It hurts! It hurts! My bones! My bones are crushing!"
Zenitsu, who had regained consciousness, screamed. He had been hit by Mukago's strike, leaving cracks in his bones here and there.
"Be quiet! We're treating you!"
Aoi slapped Zenitsu's back.
"This one has rib fractures, internal bleeding, and leg muscle tears. The boar-masked one has severe bruising around the solar plexus and swelling in the neck vocal cords. And this red-haired boy… full-body muscle pain, fatigue fractures, and a crack in his jawbone."
Ushiwakamaru delivered the diagnosis in an instant. Considering they had been injured by Mukago, the Ice Queen, it was a miracle they were still alive.
Even though she had held back, the three clearly had considerable potential.
The treatment was harsh. Especially the special medicine to draw out the demon's poisonous energy (cold energy) was so bitter it could numb the tongue.
"Nooo! I won't drink it! This tastes like dirt! It's disgusting!"
Zenitsu rolled around on the bed to avoid Kiyo, who was holding a bowl of medicine.
"Zenitsu-san! You have to drink it to get better!"
The children made troubled faces, on the verge of tears. Then, Ushiwakamaru approached with a sly smile.
"Oh my, can a grown man not even drink a little medicine?"
Ushiwakamaru instantly grabbed Zenitsu's jaw, forced it open, and poured the medicine down his throat.
He gulped… choked! Coughed!
"There, all done. Good job."
Ushiwakamaru patted Zenitsu's head, and he fainted, foaming at the mouth.
Even though she was a sexy woman showing off her chest, he couldn't get excited in this situation. The pain, combined with Ushiwakamaru's charisma, was that overwhelming.
On the other hand, Inosuke was unusually quiet. He lay on the bed, staring blankly at the ceiling.
"Inosuke-san, it's mealtime."
Aoi brought a meal tray, but Inosuke muttered in a weak voice.
"...I'm sorry. I'm weak…."
"Huh?"
"Someone like me… would be better off dead…."
Perhaps the shock was too great—having his Nichirin Blade broken by Mukago and being utterly defeated without a fight.
The wild child's spirit was gone, and he lay listless like a plucked beast.
Tanjiro, bandaged all over, watched his friends on the adjacent beds with pity.
But he too was in so much pain that he couldn't speak, only sending worried glances.
As night deepened, Kanao visited the infirmary. She checked on the sleeping Tanjiro and adjusted the IV drip.
Full-body muscle tears… burns from the recoil of using a flaming sword. Specifically, burns from grabbing a heated Nichirin Blade and frostbite from Mukago's Blood Demon Art.
Kanao looked at Tanjiro's hands. Rough, scar-covered hands. She recalled the Hashira meeting that had taken place during the day.
The boy who had been desperate to protect his sister. And Giyu's testimony that he had withstood Mukago's attack and even cut her neck.
Surviving against Mukago, an Upper Rank, and cutting her neck. Even if it wasn't a decisive blow, that's impressive. With proper training, he could reach Lower Rank level.
She understood why Akira had once taken an interest in the Kamado siblings.
Of course, he was no longer interested, but these were no ordinary individuals.
Kanao withdrew her attention and left the infirmary. As she headed back to the mansion, she thought about scheduling their rehabilitation.
Two weeks passed. Tanjiro, Zenitsu, and Inosuke's injuries had somewhat healed.
They could now get up and move around. But the real hell was just beginning.
"Starting today, we begin functional recovery training."
Aoi declared.
"This training is to restore your fallen stamina and loosen stiff muscles. Ushiwaka-san and Kanao-sama will assist."
Upon entering the training ground, the three were shocked to hear the training contents.
First, flexibility exercises. A process of forcibly tearing stiff bodies to make them flexible.
"Gyaaaah!! It's tearing! My legs are tearing!"
Zenitsu's scream echoed through the mansion. Ushiwakamaru pressed down on Zenitsu's back with her knee and spread his legs apart.
"You're being too dramatic. Muscles need to tear to stretch."
Ushiwakamaru smiled sweetly as she increased the intensity. Inosuke was naturally flexible and had no problem, but Tanjiro also had to struggle in pain.
Second was reflex nerve training.
A game where they faced each other and splashed medicinal broth from teacups at their opponent.
They had to block or dodge before the opponent lifted the cup. Their opponent was Aoi.
"Here I come!"
Inosuke charged with a shout, but Aoi's hand was faster.
*Splat!*
The medicinal broth splashed onto Inosuke's face.
"Too slow!"
Aoi said coldly.
Zenitsu also attacked, but Aoi, as Kanao's Tsuguko and in charge of the Butterfly Mansion, was very fast, having been taught by her, even if her combat power was unknown.
In an instant, Zenitsu was drenched by the medicinal broth shower.
Tanjiro followed, but the result was the same.
Third was full-body training. Essentially, a game of tag.
Training to chase or touch an opponent running around inside the training ground.
Originally, it was Ushiwakamaru's responsibility, but today Kanao specially took over.
"Start!"
Tanjiro chased Kanao using Total Concentration Breathing.
But Kanao moved lightly like a butterfly, evading Tanjiro's hands.
Always just out of reach, not quite catchable. Even after running for ten minutes, he couldn't even brush the hem of Kanao's cloak.
"Huff… huff…."
Tanjiro collapsed on the floor. Inosuke and Zenitsu were also foaming at the mouth and passed out.
"You're slow, even in collapsing."
Kanao looked down at them without shedding a drop of sweat. There was an insurmountable gap in skill between her and them.
Kanao had heard from Akira. In the original fate, she herself would have been part of the same generation as them.
But because Akira had taken her in, an overwhelming gap had emerged.
At the thought that this too was thanks to Akira's grace, Kanao naturally smiled.
"Damn… we're no match at all…."
Of course, from their perspective, it looked like a condescending expression, and Zenitsu whimpered. Inosuke returned to his "sorry for being weak" mode and hid in a corner.
But only Tanjiro's eyes remained undefeated.
I have to get stronger. To defeat that ice demon, no, to defeat the even stronger Twelve Kizuki… I must overcome this level of training!
Tanjiro clenched his fists tightly.
Following that, the fourth and final part.
Practical combat training, consisting of bare-handed sparring.
The sparring partner was Aoi.
Aoi engaging in bare-handed sparring with Tanjiro, whose will remained unbroken.
*Wham!*
"Ugh!"
"Your body should have recovered somewhat by now, right? If you're a rookie, show a bit more spirit against your senpai."
Even though Aoi was too scared to hunt demons, that didn't mean she was weak.
She only lacked the courage to fight to the death; she hadn't chosen to remain weak.
As Kanao's Tsuguko, Aoi had received various teachings from her.
"Even without a sword, you should be able to use Breathing freely! That's the basis of Total Concentration Breathing!"
Aoi, using Water Breathing while delivering kicks. Her strikes were so fast that Tanjiro could hardly react.
"Guh!"
Even though she was considered a non-combatant, in terms of skill alone, Aoi was at Kanoe rank level.
She had talent, even if she lacked courage. After all, she had passed the harsh Final Selection and was a senpai who had been in the Demon Slayer Corps longer than Kanao.
As if to show that experience and effort didn't vanish, Aoi attacked using Total Concentration Constant, creating water-like shapes with her hand strikes and kicks.
Tanjiro also tried to use Water Breathing, but without a sword, it was difficult.
The basics of Breathing started with swordsmanship and martial arts. And since Tanjiro had also learned centered on the sword, it was hard for him to focus Breathing on his bare hands and legs to imbue attacks without a sword.
In fact, this was a special case for Aoi and Kanao. Others might use wooden swords at most, but no one would bother with bare-handed fighting.
Unless you were born with Breathing like Yoriichi, or unless it was Stone Breathing which was suited for bare-handed combat, there was no reason to do so.
But ironically, this method further refined Breathing and enhanced physical abilities.
It started from Akira's idea, something no one had attempted.
If Akaza used Breathing, he'd use it bare-handed, right? Then wouldn't he wear knuckles or gauntlets? Why always imbue Breathing only in swords? If you're a demon, you don't necessarily need to use only swords.
The idea began with wondering how a bare-handed fighter like Akaza would use Breathing.
Thanks to that, at Akatsuki Trading Company, those who used Breathing utilized it in bare-handed combat as well, breaking the forms and freely handling Breathing.
A thought that came from not being Demon Slayers who hunt demons.
Demon Slayers who hunt demons practice swordsmanship; they wouldn't bother training in bare-handed combat. The method that started from Akira's quirky and, in a different sense, efficient idea was learned by Kanao and passed on to Aoi.
*Thud!*
"Gah!"
"Hoo, you still have a long way to go. Keep striving."
Tanjiro eventually lost to Aoi and fell. Aoi was worried about the level of the Demon Slayers on the front lines these days.
Unaware that she herself had become strong enough to rival past Hashira, even though she wasn't of the current generation. Since she had withdrawn from the front lines, the only ones to compare her strength to were the insurmountable Kanao, Okita, and Ushiwakamaru.
Thus, Tanjiro and his companions continued their rehabilitation training for some time.