The key lies in raising body temperature and heart rate.
When normal humans engage in prolonged, high-intensity exercise, their body temperature can rise to 38 to 39 degrees Celsius, with 39 to 40 degrees Celsius being the limit of human endurance.
The same goes for heart rate. During high-intensity or even extreme exercise, the maximum heart rate can approach or even reach 200 beats per minute.
Only a few top athletes who have undergone extensive professional physical training can withstand such a state for a certain period.
However, in addition to pushing the body's athletic state to the human limit, opening the Demon Slayer Mark requires two other crucial factors.
One is a breathing technique that has reached an extremely high level, almost reaching the 'Constant' state.
Constant breathing allows a person to use the breathing technique continuously, twenty-four hours a day, and later fully unlocks the potential of this type of breathing.
The body's state needs to reach its absolute limit, and the breathing technique also needs to reach its absolute limit.
Finally, there's the person who first awakened the Demon Slayer Mark.
For ordinary people, activating the Demon Slayer Mark usually results in a lifespan of no more than twenty-five years, with Yoriichi Tsugikuni being the only exception.
For Shimizu, that won't happen either.
It's just that the human body cannot constantly withstand such a state of limit, but for him, who has perfectly demonized his body, this burden is completely bearable.
Then there's nothing to hesitate about.
Sending Muzan another Fifth Form - Thunderclap and Flash, Shimizu gripped his Nichirin Blade tightly, his heart rate constantly climbing.
The surrounding air was continuously inhaled into his lungs through his mouth and nose. With Shimizu's powerful lung capacity, a thick white mist had already appeared around him.
Even sparks similar to those of Sun Breathing appeared, but overall, they were blue.
A faint, simple blue pattern quietly emerged at the connection between Shimizu's shoulder and neck.
The Demon Slayer Mark pattern consisted of several lines, resembling lightning bolts composed of two slightly angular flowing cloud patterns, looking somewhat like two ancient oracle bone script characters for 'electricity,' with one inverted and combined together.
Shimizu could feel a slight burning sensation coming from his Demon Slayer Mark. After the surrounding air was inhaled, it seemed as if an extremely full energy filled every inch of his body's meridians, strengthening the power of his physical body.
So, Shimizu fought Muzan even more vigorously.
The other Pillars also more or less noticed the changes in their bodies, with their strength increasing significantly.
Soon, Rui, the Upper Moon Five, was killed by the Wind and Water Pillars, who had awakened their Demon Slayer Marks.
Of the Twelve Kizuki, only the strongest, Kokushibo and Akaza, remained.
Kokushibo was still being besieged by the original three, who were among the top Pillars in terms of strength.
At this moment, all three of them had also awakened their Demon Slayer Marks during the battle.
With the three-piece set plus the sunlight lamp, they were evenly matched with Kokushibo.
The Pillars had a slight disadvantage, but it was enough to hold Kokushibo back, preventing him from freeing himself to participate in other battlefields.
The remaining Pillars all participated in the siege against Akaza.
So Akaza was getting beaten up pretty badly.
Originally, Tanjirou and Kyoujurou Rengoku were barely enough to hold him back. After awakening their Demon Slayer Marks, they had a few chances of winning. Later, the Pillars who came to support them included the Wind, Water, Mist, and Love Pillars.
Each of them had awakened their Demon Slayer Marks, not to mention that Muichirou Tokitou had also awakened the Transparent World in the grind of life and death, just like in the original timeline.
However, Muichirou Tokitou wasn't the only one who had awakened the Transparent World.
Because Kyoujurou Rengoku and Tanjirou Kamado had also awakened the Transparent World in such battles.
But there was also bad news.
That is, although Akaza was beaten very badly in such battles, he also climbed to the peak of martial arts in this world as he wished under great pressure and the threat of death, comprehending the Transparent World.
Even worse news was that when they finally cut off Akaza's head after all their hard work, they found that Akaza could continue fighting with his headless body, and even his head was growing back quickly.
"He has actually overcome the weakness of dying when beheaded... Everyone, what do you think we should do next?"
Muichirou Tokitou floated out of the clouds after cutting off Akaza's head, his expression solemn.
"Tch, could it be like that demon just now, with a real body hiding somewhere?"
Sanemi Shinazugawa blocked Akaza's punch and shouted.
"At least I haven't found any traces of other demons."
Kyoujurou Rengoku jumped out of the battle, took out a new battery, put it into the sunlight lamp flashlight tied to his wrist, and then used the scorching blade of his crimson red blade to cauterize his still bleeding eye, stopping the bleeding.
"Rengoku-san is right, I haven't found any other demons either."
Tanjirou cut off a section of Akaza's arm with Flame Dance and responded.
By now, all the remaining demons had been killed, leaving only Muzan and the last two strongest Upper Moons—provided that Tamayo and Yushiro were excluded.
In the perception of several swordsmen who had awakened the Transparent World, there were indeed only these few demons left.
"Who cares, I don't believe he can live forever! I'll keep cutting until dawn when the sun rises, and see if he dies!"
Sanemi Shinazugawa spat out a mouthful of blood, wiped the blood from the corner of his mouth, and rushed up again.
Five Pillars, plus Tanjirou, who has the combat power of a Pillar, each of them has awakened the Demon Slayer Mark and the Crimson Red Blade, and half of them have mastered the Transparent World. Even if Akaza is a demon with higher physical strength, he is inevitably suppressed until he is beheaded again.
"Akaza! I can feel that you have lingering attachments that prevent you from leaving. What is it that makes you, as a demon, unable to forget?"
Tanjirou shouted at Akaza, who was still swinging his fists.
His sense of smell is special. He can not only smell flaws in battle but also smell the emotions of others.
"I want to take step by step, to the strongest, I want to climb to the peak of martial arts!"
Akaza roared with his newly grown mouth.
"But you are already very strong. You have such great power. What are you going to do with it? Even if you become the strongest, how are you going to use it?"
Tanjirou continued to use his words.
He was still using his ability to judge the real reason why Akaza's obsession had not dissipated.
