Water Breathing is the easiest breathing method to learn among the five schools in the Demon Slayer world. Additionally, many breathing methods are derived from it. The extent to which it can be used depends entirely on the user.
In the world of Rainbow Six, doctors and several experts in human physiology studied the secrets of Tanjiro's breathing method. According to the doctor, this breathing method can make all the organs and cells of the body highly active and generate energy within a certain period of time, which can then be released by the user.
As for harm to the body? Almost none. Most cells in the human body renew every few months. Even if the energy of these cells is used up, it merely shortens the renewal period from a few months to a few weeks, which has almost no effect on life.
However, the physical fitness improvement brought by the breathing method made the doctor very excited. Yet, after researching it, he gave up this topic.
Additionally, Tanjiro's sense of smell, which is more sensitive than a dog's, intrigued the doctor. Using his sense of smell combined with breathing and modern weapons, Tanjiro discovered a very effective method: "critical hits" on vulnerable positions.
His sense of smell could detect the weaknesses of enemies.
This seemed metaphysical, but after many tests, the doctor confirmed this ability.
Consequently, in the game, the Rainbow team operators intensely trained this talent. While he may not control it perfectly, Tanjiro could still lock onto weaknesses through his sense of smell on a battlefield full of gunpowder.
The Hand Demon, the most powerful Demon on the assessment mountain, had a hard arm that could not be cut through by swords.
However...
"I smell it; you have eaten many people. You are beyond redemption. Here... here is your weakness! Rest in peace; I won't give you too much pain."
Tanjiro did not shoot first but took out a blade, signaling a hard fight ahead. The other weapons on his body, like the strange glasses on his head and the fire stick on his back, seemed non-threatening to the Hand Demon.
"Die!"
At this moment, the Hand Demon recalled the past, when it was just born and caught by the masked man in this dark forest. The surrounding wisteria flowers left it nowhere to escape, and it had to endure hunger all day long, waiting for the few people who took the trial each year.
But fortunately, it had eaten all the disciples of its mortal enemy, and today it also wanted to eat Tanjiro.
"Hehe, the little girl I met before was obviously very weak but wanted to protect everyone like you. She was torn in half by me."
"And the masked man, tsk tsk, his head was broken."
The cunning mind of the Hand Demon exceeded Tanjiro's expectations. If he were his old self, he might have been angered and rushed in recklessly. But after experiences with the Rainbow Six Team, he had matured.
Rescuing students, saving residents in slums, fighting terrorism in buildings, and even dismantling bombs and flying planes to catch criminals—all these tasks were challenging. Sometimes the enemy used teammates and civilians as threats. Initially, he was impulsive, but under the doctor's guidance, he gradually learned to stay calm.
At this moment, he recalled a conversation with the doctor.
"Doctor, why do you join the battle?"
"Why? Because I want to protect the innocent. According to psychology, I am an altruist. According to those of you who like anime and games, I am a saint, but not a saint. Remember, kindness to the abuser is persecution of the innocent. If you meet an enemy one day, just kill him directly."
The doctor knew a lot about "otaku" culture. There were operators from Japan in the Rainbow Six Team who held their drones all day and named them "wives."
For this reason, he deliberately learned about the relevant culture and confirmed one thing: that person was beyond hope and could only wait to die.
And now, Tanjiro wanted to exorcise this Hand Demon!
Taking a deep breath, ripples like water appeared on his weapon. The Hand Demon sensed the change in Tanjiro's breath, and the mouth covered by its large hand revealed a bright smile.
"Just get angry! Then become my food in your rage!"
No matter how strong Tanjiro's predecessors were, they all became the Hand Demon's food. It believed Tanjiro would suffer the same fate and become part of its strength.
"Water Breathing Fifth Form..."
Tanjiro had already rushed up: thirty steps, twenty steps, ten steps. The distance between the man and the Demon was shrinking. At such a close range, the Hand Demon felt it couldn't miss any of its skills. But it didn't matter. It had patience. It couldn't be harmed by the blade in Tanjiro's hand. It would wait for Tanjiro's attack to fail, then strike.
Nine steps! It saw Tanjiro raise the blade.
Eight steps! It saw Tanjiro put away the blade in one second.
Seven steps! Tanjiro took out the strange weapon from his back and aimed it.
"Sorry, times have changed!"
Tanjiro looked at the neck protected by the Hand Demon's oversized arm. Despite the strong defense, he detected a "weak point" through his sense of smell.
"Here, you can hit critically!"
This term, learned from Liu Yuan and Kisara at the internet café, suggested Tanjiro's sense of smell improved his critical attribute.
"Da Da Da Da!"
As they say, seven steps away, the gun is fast, and within seven steps, the gun is fast and accurate.
Tanjiro fired, and flames sprayed from the M249 in his hand. The 7.62mm armor-piercing bullets easily penetrated the demon's proud defense. With a machine gun's initial velocity of 900 meters per second, there was no chance to react at close range.
According to the doctor, no creature on earth can avoid the shooting of a light machine gun within seven steps at the moment of firing.
Unless one dodges in advance, there's no escape.
Cure? Tanjiro would not give him that chance. The steel bullets tore through the Demon's flesh and blood completely. According to the doctor, this process was not painful.
A horizontal sweep, and the Hand Demon's head fell off instantly.
These armor-piercing bullets could penetrate steel plates. Perhaps Muzan Kibutsuji could withstand their continuous firepower through sheer resistance, and even the upper ranks might hold out for a while, but this ordinary Demon stood no chance.
A hundred bullets were poured out in less than ten seconds. From the beginning of the shooting, the Hand Demon felt its body completely out of control. Even as Tanjiro stopped attacking, it was still in a daze. But at this moment, its head had fallen off.
"What's going on?! What is that?!"
The Hand Demon wanted to taunt, but before it could say anything, its head was shot off.
As the head fell to the ground, Tanjiro made the final finishing blow.