Afternoon,

In a big mansion.

Three people were stretching their bodies,showing painful expressions.

These three were Tanjiro,Harada and Inosuke.

Today,it had been three weeks since they came here,for the first two weeks they recovered from their injuries to a certain extent and then their rehabilitation training started.

There were three girls there as well,namely,Naho,Sumi and Kiyo.They were helping Harada and the rest to strech their bodies in different positions,it was simmilar to a massage,but a very painful one.

After doing this,they would have to play a certain game with Kanao Tsuyuri to train their reflexes.

Although it was a game,it was countless times harder than any other game a human could possibly think of.

And then came the Tag with Aoi Kanzaki and Aoi,it was actually very enjoyble training compared to others.

Harada and the rest would have to do this for a few hours.

Zenitsu had to drink bitter medecines as he was on the verge of becoming a spider.

Due to which his limbs were very small now,so Zenitsu hadn't joined us yet,he was scared of the pain that the traing will bring.

Thus he was given an extra week for resting.

"I can feel my body getting stronger everyday!" Harada thought.

"This is the same as the last time when I was trained by Urokodaki-san,the first day,my entire body was hurting,but from the next day,my power increased quite a bit.

This means the more strain my body experiences,the stronger I get! That would mean,as soon as I learn the constant breathing,I will be nearly unbeatable." Harada analysed the changes in his entire body.

He didn't have a normal body,he had a body with nearly unlimited potential as it was given to him by the god as one of his wishes.

But he couldn't unlock that potential automatically,he needed training and experience,which he was getting now.

"I'll be the strongest demon slayer ever!" Harada thought.

He didn't need to worry about Tanjiro or Nezuko's safety,and as long as he kills the demons,he is protecting them in a certain way.

What was constant breathing?

This breathing expands the user's lung capacity.

By constantly using the breathing technique, the user's base stamina gradually grows. According to the attendants of Butterfly Mansion, being able to use Total Concentration: Constant makes all the difference in the world for a demon slayer.

Maintaining the Total Concentration Breathing state at all times is extremely difficult and taxing on the body. It requires vigorous training to master this form by expanding one’s lungs and making them strong enough to perform the breathing technique around the clock.

It is an advanced and esoteric breathing technique where a user inhales the maximum amount of oxygen within a specific breath pattern to raise their physical and mental prowess to their utmost limits. The effects include a plethora of enhanced physical and mental abilities, like superhuman physical characteristics (i.e. Strength, Speed, Stamina, Durability and Agility), faster thought processes, concentration and information processing. This technique is also capable of clotting wounds from severe injuries and slowing down the circulation of poison in the bloodstream.

"If I could learn it."

Harada couldn't help but shiver from excitement from the mere thought of using that technique.

Water's breath and total concentration techniques are two completly different things.

Water's breath can be used when fighting demons while Total concentration breadth:constant had other effects.

When he was younger,his concept of water's breath and total concentration was quite inaccurate.

He thought that Water's breath and total concentration breathing were the same thing,but when he was trained by Urokodaki-san about the breathing techniques,he discovered how ignorant he was.

..............

After a week.

From this day onwards,Zenitsu will join the rehabilitation training.

He was very scared about the training,because the first day when I,Tanjiro and Inosuke returned from the training,we looked as if we were dead inside.

"Zenitsu-kun,it's your first day in the training do I'll explain to you,the first thing they do is give you a massage,with their own two hands!, then you play with teacups with them and lastly play tag with them,if you don't believe me then see it for yourself today" Harada told him the details of the training in a low voice with a smile that only men understood.

"Eh,are you really saying the truth,Harada-sama?" Zenitsu asked surprised.

"Why would I lie to someone younger than me?" I said with a proud expression.

"Okay then!!" all of a sudden,Zenitsu felt a surge of power in him.

And then the same things happend as I remembered from the anime.

Zenitsu enjoyed the training as much as he could for a few days,but then,came the Kanao-san,to play the teacup game.

Nobody could defeat her at all.

Even after a few days,nobody could.

We were drenched in tea from head to toe everyday.

Inosuke didn't like losing so many times so he started sulking and stopped coming to training.

And soon,Zenitsu also gave up.

Now only I and Tanjiro were left.

After ten days,after losing the teacup game as usual,we were going to our rooms.

Suddenly,

"Harada-san,Tanjiro-san" those three girls called out to us.

"Ah,you starled me for a bit" I said.

"What is it?" I asked in a gentle voice.

"Can you both do the total concentration breathing all day?"

"Can you also do it even when you're sleeping?" They asked innocently.

"Total concentration breathing is difficult to maintain even for a short while,It is impossible for me to do it all day" Harada admitted.

"Then we can help you learn!" the three girls said enthusiastically.

"Okay then,we'll give it a go,okay Tanjiro?" I asked Tanjiro.

"Yes,Nii-san,let's give it a try" He replied.

..............

The next day,

In the courtyard of the mansion.

Two boys,covered in sweat,were talking in low voices.

"Argh,I feels as if my lungs will explode and my heart will come out of my ear" Harada said while struggling to stand.

"Ah,I can't imagine how they do it all day" Tanjiro whilelying on the ground.

Just as we were saying that,the three girls came to us.

"Harada-san,Tanjiro-san,we are here to help you,you see,the reason you may be feeling like is because the capacity of your lungs might not be enough" they said.

"Wha! I thought I had enough lung capacity"

"I thought my body had become strong enough,but I guess that's not true." Harada thought.

"When Shinobu-san and Kanao-san were doing their "total concentration breath:constant" training they used to bkow air in these gourds and make them explode wtih the sheer amount of air in their lungs" the three girls said in unison.

Tanjiro was horrified to see the gourds and hear what he had to do with them.

But I knew how to do it.

"Hm,first let's increase our lung capacity" I suggested.

"Great idea,nii-san" Tanjiro replied.

................

After 15 days,

"Nii-san,I think we should start our training today" Tanjiro came to me,looking more motivated than ever before.

"Perhaps,he met Shinobu last night,just like in the anime eh" I thought.

These 15 days,all we did was training to increase our lung capacity.

"Yes,I think so too" I agreed to finally start our training.

Today,all we both did was focusing on maintaining our concentration breadthing.

Even when we slept.The three girls would make sure that we were breadthing in the correct way,otherwise,we would be beaten by sticks.

The first day,

It was basically torture for our lungs.

The second day,

It was slightly eaiser than the first day yet it was very difficult.

The third day,

Today,Zenitsu and Inosuke joined us as well by being motivated by seeing us.

They also tried to increase the capacity of their lungs and started learning the total concentration breathing.

After 9 days,

Maintaining the breathing technique for all day was very easy for all of us,especially me,I was constantly sweating every second.

Every second my body would feel lighter,yet stronger,I could feel my focus increasing to an inhuman level.

Today,I eaisly beat Kanao-san in the teacup game.

After 16 days,

It's been around a month since we came to the butterfly mansion.

I can now maintain total concentration breadth for all day all night.

There wasn't even a single moment when I made a mistake.

Every second I could feel my stamina,strength,flexibility,reflexes improve little by little.

Tanjiro,Inosuke,and Zenitsu also learned the total conecntration breath;constant.

Today,our swordsmiths were coming to bring us our swords.

"It's a good thing that I didn't waste a single moment in this masion.

To be continued.....