Selfless State

The Selfless State (の), also known as the Realm of the Highest or the Domain of Supremacy, is a state of being in which one completely erases their battle spirit and is implied to be the zenith of physical combat.

Overview
The Selfless State is a supernatural and esoteric state of being in which one completely erases their battle spirit, will to fight, bloodlust, anger, hatred, malevolence, drive and animosity. Once in this state, the user's behavior becomes incredibly tranquil and focused, often being compared to that of a plant.

The existence of this state of being remains shrouded in obscurity, known only to a limited few with profound understanding, and even fewer possess the capability to attain it. Throughout his centuries-long existence, Akaza has never encountered a human devoid of a battle spirit, as even infants emit a faint trace of it.

In combat
Although it does not enhance one's own combat prowess, it is regarded as the the highest state of physical combat one can ever achieve. It is extremely effective against high-level combatants who rely on various forms of extrasensory perception to detect malice, aura or fighting spirit. The incapacity to perceive the battle spirit of an individual in the Selfless State induces sensory confusion, resulting in a disorienting experience akin to battling against an inconspicuous intruder, like an out-of-place plant.

By combining the Selfless State with the Transparent World, one could strike a decisive and lethal blow by anticipating the vital points and movements of their opponent through slow-motion perception and precognition, as well as skilfully evading detection of their own attacks.

Unlocking
Based on insights Tanjuro Kamado shared with Tanjiro, one must engage their five senses and cultivate an acute awareness of their entire being, down to the tiniest blood vessel. By focusing on precise breath control, movements, and sensations, they can unleash maximum strength with minimal effort. As a result, the mind transcends visibility and enables the closure of all senses, leading to a state of complete detachment from oneself.

Yoriichi Tsugikuni
When Yoriichi encountered Muzan Kibutsuji for the first time, he instantly realized the purpose of his life is to kill the Demon Progenitor, and was filled with unwavering determination to accomplish this. Yet, in Muzan's retelling of the encounter, he felt that the swordsman looked weak. He could not detect any ambition, willpower, hatred, and killing intent in him. Because of that, Muzan underestimated him and was totally stunned when Yoriichi easily decapitated and slashed him, giving him wounds that continued to burn his flesh for over hundreds of years. Yoriichi either remained in a perpetual state of selflessness, or swiftly entered it upon encountering Muzan, effectively eluding Muzan's ability to detect his intentions.

Tanjuro Kamado
In Tanjiro's memories of his father, Tanjuro remained perpetually in the Selfless State. He was like a plant, always gentle and would never have any emotional outbursts, which never changed in the slightest until his death. His voice was as calm as a murmuring river and he always had a soft smile. Ten days before he succumbed to his death, he demonstrated to Tanjiro how to kill a bear while remaining in the Selfless State. Tanjiro sensed how his father's smell never wavered, there was no hesitation or fear in him before or after cutting off the bear's head, nor was there any intent to kill. Tanjuro still maintained his usual plant-like presence the entire time.

Tanjiro Kamado
During the final battle with Akaza, Tanjiro noticed how Akaza is able to react to attacks highly accurately, even when they are from behind or from blind spots, as if they're being attracted by magnets. Remembering Akaza's words about Kyojuro Rengoku's battle spirit and Inosuke Hashibira's explanation, Tanjiro discerns that Akaza must be able to sense his fighting spirit using his compass technique. Using the insights Tanjuro provided him during his childhood, Tanjiro entered the Selfless State and entirely evaded Akaza's detection of his presence. With the combined use of the Selfless State and Transparent World, he then successfully severed Akaza's head. Akaza was bewildered by his inability to perceive Tanjiro's fighting spirit. He likened the experience to engaging in combat against a mere plant.

Trivia

 * The Selfless State is also often referred to as the  State of Anattā, a state with striking similarities to the Selfless State which works as a state of nothingness where one is so focused on the fight that they become completely detached from everything else and can engage in combat without wasteful thoughts and movements. The nothingness one experiences in this state is akin to plants on a battlefield, where opponents are always on the constant lookout for moving targets/animals while presenceless plants in the background are usually completely ignored. Thus, to be in the State of Anatta is to "be" the plants on the battlefield, to mesh oneself in the background so much until their opponents don't notice them until it's too late.
 * Selflessness stands in stark contrast to "selfishness," as it entails a genuine focus on the needs and desires of others rather than one's own. Those who embody true selflessness exhibit a profound lack of self-concern, devoid of personal agendas or biased attachments to their surroundings. In Buddhism and Taoism, an individual who attains true selflessness navigates the world as though absent, liberated from self-centeredness and effortlessly harmonizing with their environment.
 * Kagaya Ubuyashiki's aura highly resembled that of one being in the Selfless State. Like Tanjuro, Kagaya maintained a calm and gentle demeanor throughout his life. Exhibiting extraordinary levels of selflessness, he genuinely cared for others, exemplified by his meticulous memorization of each member's name within the Corps. Furthermore, he diligently paid daily visits to the cemetery of fallen members until his illness rendered him immobile. He consistently prioritized the well-being of others, valuing the greater cause of humanity above his own life. When Muzan came to Kagaya's house to kill him, Muzan noticed that Kagaya faced him with the smile of a Buddha. Muzan could not detect any murderous intent in Kagaya at all. Only after the explosion did Muzan realize the depth of the hatred and anger Kagaya had towards him, which Muzan describes as being like a viper that was coiling in his dead, black stomach. Muzan was in awe at how stunningly Kagaya hid his intent. However, it is not confirmed with conclusive evidence that Kagaya did in fact enter the Selfless State.

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