Sabito

Sabito was a former apprentice of Sakonji Urokodaki. He appeared to assist Tanjiro Kamado in his preparations for the Final Selection exam.

Appearance
Sabito was a fair-skinned young man with a large scar running from the right corner of his mouth to his right ear and kind, cat-like eyes of a grayish lavender color, a horizontal bar of much paler purple visible across them near the bottom. He had thick, spiked, peach-colored hair of varying lengths, the longest reaching his shoulders, that he wore messily down with side-micro bangs over the left of his forehead.

Sabito wore a green yukata, patterned with a geometric hexagon design of yellow and a darker green, like Giyu Tomioka, tied off at the waist with a piece of black fabric, below which he sported a pair of hakama pants and over which a plain white haori. Around his calves, he wore two pieces of cloth, that bore the same design as his yukata, which his pants were tucked into, as well as black socks and a pair of Japanese sandals on his feet. As with the rest of Sakonji Urokodaki's apprentices, Sabito's white warding mask, hand-carved by his master himself, took the shape of a fox's face, he decorated by a large scar in the same place as the one on his face. The mask's eyes and nose were of a dark green while the ears were more of a gray-red, and it was secured around his face by a thick piece of red rope around his head, the ends of which hung down from behind each of his ears.

Personality
Sabito was a serious young man who believed that all of his actions should be becoming of a man. He was seen as a ruthless mentor during his time training Tanjiro Kamado, who was always quick to point out his flaws and refused to acknowledge him as a man. When asked about defeating the Hand Demon, Sabito appeared to have a pessimistic view on conflicts, saying he believed that no matter how hard someone tries it will never be enough to take the beast down.

Even so, Sabito entrusted his will to Tanjiro and was happy when he surpassed him as Sakonji's strongest student, openly acknowledging that Tanjiro was the toughest of them all and proudly leaving the lingering will of all Sakonji's lost children to him.

History
Not much is said about Sabito's history, but Sabito encountered a powerful morphed Demon who desired to devour all of Sakonji's students. In an attempt to kill it, Sabito's blade breaks on the demon's thick neck, and he dies in the Demon's hands. Sabito's soul return to Sagiri Mountain, as he can't rest due to his failure and Sakonji's grief.

Final Selection Arc
Unable to rest after failing to return to Sakonji, Sabito and Makomo's souls find their way back to Sagiri Mountain, where they reside from then on. Sakonji eventually takes on a new student named Tanjiro, and, after one and a half years of training, Tanjiro is still unable to pass Sakonji's final test: splitting a boulder using his sword.

Sabito sits atop the boulder, appearing before Tanjiro as he laments over his lack of progress and tells him that a man should grieve in silence. He attacks Tanjiro and kicks him aside after a short clash of their weapons, saying that Tanjiro is slow, weak, and immature and telling him these are not the qualities of a true man. Tanjiro asks Sabito what he's doing, and the latter responds with the same question, continuing to ask how long Tanjiro plans to remain on the ground. After he gets up, Sabito asks him to come and fight, but Tanjiro expresses concern over using a real katana against Sabito's wooden sword. Amused by the fact that Tanjiro thinks he can harm him at his current skill level, Sabito laughs before rushing at his opponent.

Sabito's wooden blade pressures Tanjiro just like a real one would. The masked boy claims he's the stronger of the two and denies the idea that he might get hurt, revealing that he already sliced the boulder before. Sabito leaps through the trees, using his extreme agility to throw Tanjiro off before striking him down. Sabito tells Tanjiro that he hasn't mastered a single form of Total Concentration Breathing, claiming that Tanjiro has only memorized the practices and needs to slam those lessons into his flesh instead if he wants to learn them. He pressures Tanjiro with a flurry of slashes and demands that he never forget the secrets he learned from Sakonji.

Tanjiro claims he's working hard but can't make any more progress, and Sabito tells him to act like a man and go further to surpass his limits. He wants to see what Tanjiro is capable of in this fight and defeats him shortly after using a powerful uppercut swing. Sabito then entrusts the remainder of Tanjiro's training to Makomo.

Tanjiro continues to challenge Sabito throughout his training but isn't able to win, or at least not until six months later. During their final duel, Sabito brings a real katana instead of a wooden one, and, on that day, Sabito finally says Tanjiro has the look of a man. The fight ends instantly, as Tanjiro's blade finally reaches Sabito first, splitting his mask. Sabito's face gets revealed, and he's smiling, proud of his successor. He disappears and Tanjiro realizes that he's finally sliced the boulder.

As Tanjiro bides farewell to Sakonji, he asks him to greet Sabito and Makomo for him, leaving Sakonji confused. Hinting at the fact that the two were ghosts, Sakonji wonders where Tanjiro got those names from. After Tanjiro leaves for his Final Selection, Sabito sits atop the boulder, continuing to watch over him with Makomo, who asks if Sabito thinks Tanjiro can avenge their deaths. Sabito says he isn't sure because they lost despite their bests efforts.

Tanjiro learns the truth about the deaths of thirteen of Sakonji's children at the hands of the morphed demon. Enraged, Tanjiro rushes in to attack recklessly, but Sabito reminds him to calm down because his breathing is uneven. He asks Tanjiro to forget about the others for now and focus on the task at hand. Makomo starts to lose hope and questions if Tanjiro will die too. Sabito tells her the outcome can go either way, however, there is one irrefutable fact: Tanjiro is the man who sliced the largest, toughest boulder of all. The Hand Demon believes he can defeat Tanjiro the same way he did Sabito, but Sakonji's newest student slays the demon and avenges all the fallen children.

Tanjiro wins and the souls of all of Sakonji's children can rest in peace. Satisfied that no more lives were being lost to the demon and that their master would get one of his children back, Sabito leaps off the boulder and disappears into the mist, bidding farewell to Tanjiro.

Abilities
Sabito is regarded as Sakonji's most powerful former pupil, succeeded only by Tanjiro; the Hand Demon even noted that Sabito was the most powerful disciple of Sakonji's that he had killed. Tanjiro has stated that Sabito would have likely been an amazing swordsman if he had survived.

Swordsmanship
Sabito was a very skilled swordsman, as seen during his Final Selection exam, in which he was able to kill nearly all of the Demons on the wisteria flower mountain single-handedly and save all the other participants, a feat that even Tanjiro was unable to accomplish as he was busy protecting himself. Throughout Tanjiro's training, Sabito was also able to repeatedly defeat him while wielding a wooden sword, even though Tanjiro was using a real blade, and, during their first battle, Sabito showcased enhanced speed, agility, and reflexes that easily outclassed those of Tanjiro at the time. It eventually took Tanjiro six months of training before he was able to defeat Sabito.

Katanas: Sabito possessed both a wooden sword and a real sword. He was very proficient with the wooden sword against Tanjiro, even though the latter was wielding a real blade.

Water Breathing: Sabito was a skilled practitioner of Water Breathing, which he used to single-handedly kill all the Demons inhabiting the wisteria flower mountain during his Final Selection exam."First Form: Water Surface Slash - The user generates enough momentum to create a powerful single concentrated slash.""Second Form: Water Wheel - The user leaps and vertically spins forward in the air while releasing a flowing attack in a circular motion.""Second Form: Improved - Lateral Water Wheel - The user uses the Second Form: Water Wheel in a horizontal spin.""Third Form: Flowing Dance - The user swings and bends their blade in a winding motion along with their body and dances in a flowing pattern, slicing everything in its path.""Fourth Form: Striking Tide - The user makes multiple consecutive slashes while twisting their body and sword in a flowing fashion to deliver multiple blows simultaneously.""Striking Tide - Turbulent - An improved version of the Fourth Form: Striking Tide. The swordsman increases the number of consecutive strikes and slashes along with improving its accuracy to contact a specific target during a chaotic situation.""Fifth Form: Blessed Rain After the Drought - The user changes the grip on their sword and decapitates the opponent in a single flowing strike that causes little to no pain. It is a “sword strike of kindness” used when the enemy willingly surrenders.""Sixth Form: Whirlpool - The user fiercely twists their upper and lower body, creating a whirlpool of air that cuts anything caught in it. Its effect and efficiency are enhanced underwater, where the user can draw water around their weapon to enhance their slashes.""Whirlpool: Flow - A combination of Third Form: Flowing Dance and Sixth Form: Whirlpool. The swordsman combines the footwork from Flowing Dance and the twisting aspect of Whirlpool, resulting in the swordsman performing an attack around the user and conjure a twisting, swirling, the vicious flow of water to redirect projectiles from multiple angles.""Seventh Form: Piercing Rain Drop - The user performs a fast and accurate stab, capable of reducing the impact of a moving target. The fastest and only thrusting technique of this breathing style.""Seventh Form: Piercing Rain Drop - Curve - A modified strike that hits in an arc from an angle corresponding to the sword's structure to minimize the impact of a moving target.""Eighth Form: Waterfall Basin - The user cuts the target vertically in a flowing motion which is most effective when they are falling downward.""Ninth Form: Splashing Water Flow - The user changes their footwork in a way that minimizes the landing time and surface needed when landing, allowing the user to move without limits. Ideal when fighting in a place with no solid foothold.""Ninth Form: Splashing Water Flow - Turbulent - An improved version of Ninth Form: Splashing Water Flow.""Tenth Form: Constant Flux - The most powerful Water Breathing technique. The user performs a continuous flowing attack which takes a form of a water dragon that increases in strength and power with each rotation."

Trivia

 * He is considered the best student among others under the guidance of Sakonji.
 * His name contains the kanji for "rust" (錆 sabi?) and "rabbit" (兎 usagi, to?).

Reference

 * 1) https://kimetsu-no-yaiba.fandom.com/wiki/Sabito