Fox Demon: Heaven rewards diligence; I will eventually achieve divine mastery of martial arts.

You've hit a bottleneck.

Lin Yu's calm voice echoed in his mind.

"Bottleneck?" Tanjiro Kamado was stunned for a moment, then became somewhat excited. The cultivation technique given to him by Lin Yu naturally contained a detailed description of the bottleneck.

This is a threshold.

Human beings possess limitless physical potential, yet they are also bound by limitations. If humanity were to cross this threshold, the world would be their oyster, but this threshold often seems like an insurmountable chasm, hindering countless people throughout history.

"So, Master, how can I break through this barrier?"

Tanjiro Kamado asked somewhat nervously, "Although the technique describes the bottleneck, it doesn't provide detailed methods for overcoming it."

That's for sure. After all, in the world of fox spirits, while it's a bit difficult to generate internal energy, the difficulty lies in the early stages of physical training. As long as you train your body well, breaking through the bottleneck here will naturally be a natural outcome.

This world has a natural suppression of transcendental energy.

The seemingly limitless power of emotion, when applied to Tanjiro Kamado, could only slightly enhance his physical body.

Previously, Lin Yu's mental and emotional power were able to work because his own energy level was too high, which allowed him to easily crush them.

But for Tanjiro Kamado from the original world, this bottleneck was naturally incredibly strong.

Demons, on the other hand, break through this bottleneck through genetic mutation. However, the world is always fair.

Power that is easily obtained will eventually turn against you.

In the future, the evil spirits will face even more formidable obstacles.

"There is a way to help you break through this bottleneck, but it will be life-threatening. However, as long as you get through it, your strength will grow rapidly in the future."

Lin Yu said.

Tanjiro Kamado fell silent.

Death seemed a distant concept to him.

Moreover, his death might leave Nezuko without him as her only family member, but Nezuko and Sakonji Urokodaki are getting along very well now.

If he dies, Urokodaki Sakonji will definitely take good care of Nezuko.

He could sense that he was very strong now, but he always felt that he wasn't strong enough.

For example, if he were to face Giyu Tomioka now, he would likely win, but he would still be at risk of losing.

In the past few days, he had learned from Urokodaki Sakonji that Tomioka Giyuu was very strong, but there were also many demons stronger than Tomioka Giyuu, not to mention the existence of demon lords that were not recorded.

So, what are his true chances of winning against someone who might be even stronger than Giyu Tomioka?

The answer is obvious.

Tanjiro Kamado raised his head and said firmly:

"I'm willing, Master. I'm willing to do anything to become stronger."

"Alright, take the medicine I asked you to brew earlier to the Cold Pool in the southwest of Narrow Mist Mountain."

Lin Yu said.

Tanjiro Kamado nodded and rushed into his room to retrieve a bottle of dark, almost solidified medicine.

This was made by him under Lin Yu's guidance using a variety of medicinal herbs he found in the Narrow Mist Mountain.

It took three whole days to brew this potion.

At that time, he didn't understand what the potion was for. Now he understands that Lin Yu had already begun to plan for his current bottleneck back then.

It turns out that my master always believed he would choose risky methods, so I must not let him down!

As Tanjiro Kamado ran towards the cold pond, he made a silent resolution.

……

Mount Sagiri isn't very high in altitude, but there's a cold pool on the mountainside in the southwest direction.

The cold pool was deep and unfathomable; even in the height of autumn, the temperature felt like early winter.

Tanjiro Kamado stood by the cold pond, somewhat nervous.

"Drink the medicine."

Lin Yu's voice drifted over.

Without hesitation, Tanjiro Kamado tilted his head back and poured the medicine into his mouth.

The medicine was viscous and, unsurprisingly, extremely bitter. In addition, it had been sitting for too long, which gave it an astringent taste in addition to its bitterness.

But once it enters the throat, it transforms into a warm current that flows down in a single stream.

boom!

It's like pouring a pot of hot oil on a fire!

It seemed as if a flame was being ignited inside Tanjiro Kamado's body.

The flames spread like wildfire, reaching his entire body at the speed of light.

Countless tiny, scorching flames burned his internal organs, and those flames, which seemed capable of melting steel, surged and crashed wildly!

"what!"

The flames spread to Tanjiro Kamado's forehead, and he couldn't help but scream. His fragile head felt like it had been branded with a hot iron, and his vision was filled with crimson.

At this moment, it can be clearly seen that Tanjiro Kamado's body surface is as red as a boiled shrimp shell.

"Ahhhh!"

The howl was deep and piercing, like that of a wild beast. On Tanjiro Kamado's exaggerated muscles, veins bulged out like red-hot iron wires, covering his entire body.

The burning sensation and pain were slowly eroding Tanjiro Kamado's sanity.

At this moment, Lin Yu made his move, his spiritual power transforming into a point of light that flew into Tanjiro Kamado's soul.

Tanjiro Kamado, who thought he was in a sea of ​​fire, suddenly felt a block of solid ice appear in the fire.

Although it was strange, he instinctively grabbed the piece of solid ice.

However, after grasping it, Tanjiro Kamado suddenly regained some clarity of mind, and at the same time, he heard a distant voice seemingly coming from within the solid ice:

"...jumped into the icy pool..."

A cold pool?

Where is that?

Tanjiro Kamado was somewhat puzzled, then suddenly remembered that he was preparing to break through his bottleneck.

When he realized this, his vision instantly changed from a crimson blur to a normal view.

Although the heat was still unbearable, he had regained the ability to think.

And that distant voice was Lin Yu's voice.

Without a second thought, Tanjiro Kamado jumped straight into the icy pond.

He knew very well that Lin Yu would never harm him, after all, Lin Yu was so powerful that there was no need for him to go through such a long process to harm him.

So he had completely trusted Lin Yu for a long time.

Even if he were facing a mountain of knives and a sea of ​​fire, he would not hesitate.

With a splash, Tanjiro Kamado fell into the icy pond.

He sank rapidly like a stone, and the intense heat within him seemed to be relieved somewhat.

But at some point, Tanjiro Kamado felt his body burst into flames once again.

The flames melted away the surrounding chill, and the intense heat returned.

At that moment, Tanjiro Kamado, with his last remaining sense of consciousness, felt his feet touch the hard ground.

He hit rock bottom.

At the same time, Lin Yu's voice echoed in his mind again.

"Practice the boxing techniques while simultaneously shifting your external breathing to internal breathing."

Upon hearing Lin Yu's voice, Tanjiro Kamado's mind was immediately filled with doubt.

He understood each of Lin Yu's individual words, but he couldn't understand them when they were put together.

Breathing can only be outward breathing; what is internal breathing?

He could only swing his fists instinctively, little by little. Guided by the movements, the flames raging within his body found direction, but the intense heat remained undiminished.

The sound came again, but this time it was more distant:

"...Imagine a ball of air in your chest, inhale it..."

Is there a ball of air in my chest?

Tanjiro Kamado couldn't figure out who was speaking; he just felt it was extremely familiar.

But then he suddenly realized something.

painful.

too painful.