Sanemi is a tall, muscular, and slender man with spiky white hair and large eyes. His face and body are covered with scars, accrued over his many years of fighting demons. He cuts his hair short somewhere in between the Functional Recovery Training Arc and the Demon Train Arc.
Sanemi is abrasive, hot-blooded, and stubborn, oftentimes impulsive and quick to lash out. The only person he displays reverence towards is Kagaya Ubuyashiki, and only after realizing the man was much more than his outwardly appearance suggested.
Sanemi's cold, rude, dismissive behavior is the result of losing too many people he cared about in the past. When Genya joins the Demon Slayers in search of Sanemi, Sanemi hurls verbal abuses at him, but Tanjiro Kamado is able to tell Sanemi didn't truly hate him; and in fact still bore the same brotherly love he had for him in childhood. This was however never expressed outwardly as he tried to push Genya away from him and the Demon Slayers so he wouldn't be exposed to danger.
Because of all those he lost to demons, he harbors a deep hatred towards demons and is convinced that humans and demons can never coexist. When Sanemi makes up his mind about something, it is extremely difficult to dissuade him— he doesn't believe Tanjiro's insistence that Nezuko Kamado doesn't eat humans, and moves to prove his own point by stabbing through the box with Nezuko inside. After riling her up, he slashes his own arm to try and bait her into attacking him due to his rare blood's effect. Even after she doesn't, and Kagaya uses this as proof Nezuko won't attack humans, Sanemi doesn't truly accept the Kamado siblings.
Sanemi was the eldest son of seven children and lived with both of his parents. Their father was abusive, constantly lashing out at the children and their mother until one day, he was stabbed and killed by someone with a grudge against him. Afterwards, Sanemi and Genya resolved to support their mother and family.
One day, Sanemi's mother failed to return home, so Sanemi left to search for her. At some point, he found her and realized she became a demon, but couldn't stop her from returning home and killing five of his siblings. Just before she could kill Genya, however, Sanemi tackles her through the window to the street below with a knife in hand. In the ensuing fight, she gave him the two large scars across his face, and his marechi blood—which disorients demons and makes them act intoxicated—gave him an opening to cut her down.
When Genya runs into the street to find a doctor for his grievously-injured siblings, he finds Sanemi with their mother lying dead at his feet. Panicking, and not knowing that the "wolf" that attacked them was their demonified mother, Genya screams and accuses Sanemi of murdering her. Sanemi, still in shock, became partially colorblind as their mother dissolved in the sunlight.
After that, Sanemi abandoned Genya and began to hunt demons on his own with suicidal devotion. Without knowledge of Demon Slayers or Nichirin Blades, Sanemi instead armed himself with a multitude of weapons and fought demons at night, incapacitating and capturing them until daybreak, then stringing them up to let the morning sun killed them. Despite this crude and reckless battle style, he managed to survive thanks to sheer luck and the unique aroma of his blood.
While wandering the land hunting demons, he eventually met a legitimate Demon Slayer, Masachika Kumeno, who helped him and introduced him to a proper trainer. Upon completing his training, the two of them teamed up to defeat the then-Lower Moon One of the Twelve Demon Moons. However, Kumeno lost his life in the battle, and only Sanemi was promoted to the rank of Wind Pillar. At the time of his promotion, Gyomei Himejima, Kanae Kocho, Tengen Uzui, and Giyu Tomioka were already Pillars.
Bitter over Kumeno's death, Sanemi takes his anger out on Kagaya, accusing him of happily giving orders from above while the Demon Slayers bleed and die for his cause. To his surprise, Kagaya takes the criticism gracefully before mentioning Kumeno by name; Kanae then informs him that Kagaya has memorized the names and backgrounds of every single Demon Slayer who has died since he became leader. This discovery, and reading Kumeno's will given to him by Kagaya, gives Sanemi a newfound respect for the leader of the Demon Slayer Corps.
Abilities and Powers
- Master Swordsman: Being a Pillar of the Demon Slayer Corps, Sanemi is one of the most powerful and skilled swordsmen in the entire organization. Sanemi's skills and sword techniques are incredibly powerful and refined, impressing even Upper Moon One Kokushibo, a Demon with hundreds of years of skill and experience behind him.
- Intoxicant Blood (Marechi): Sanemi's blood was revealed to be one of the rarest blood types, making it incredibly intoxicating and mouth watering to demons. It is also unique due to its intense potency that the smallest whiff of his blood immediately causes demons to salivate and lose focus, as his blood was able to affect the strongest of the Upper Moon Demons, Kokushibo. So far, the only demon who is immune to Sanemi's blood is Nezuko, due to her own strong conviction and will not to eat humans that was even further cemented and strengthen by the hypnosis planted in her brain by Sakonji Urokodaki.
- Muscle Control: Sanemi has also shown the ability to manipulate his own muscles to close up and prevent fatal and mortal wounds from opening up and bleeding out during mid battle, as seen when he was fatally slashed and cut up across his abdomen by Kokushibo, he was still able to fight on by manipulating his own muscles to close up his wounds.
- Demon Slayer Mark: Later during battle against Upper Moon One, Kokushibo, Sanemi awakened his own Mark that takes on the appearance of a single Paper Oragami Windmill with two dots on both sides on his right cheek. The mark dramatically increases his power and abilities, as seen when Sanemi was still able to fight and contend with Kokushibo on even ground, despite being grievously injured and slashed across his abdomen. This shows that his physical endurance, strength, and tolerance to pain have been dramatically increased. However, he couldn't land a significant hit on Kokushibo without assistance from Himejima and Muichirou. In addition, he would have been put into a near-death state twice by Kokushibo if it weren't for Muichirou and Himejima's intervention.
- First Style: Dust Whirlwind Cutter (
壱ノ 型 鹿 旋 風・ 削ぎ Ichi no kata: Jin senpū・sogi?) - Sanemi dashes forward in a cyclone of slashes.
- Second Style: Claws-Purifying Wind (
弐ノ 型 爪 々・ 科 戸 風Ni no kata: Sōsō - shina to kaze?) - Sanemi sweeps onward and creates four claws-like slash to enemy.
- Third Style: Clear Storm Wind Tree (
参ノ 型 晴 嵐 風 樹San no kata: Seiran fūju?) - Sanemi sweeps his sword in circular movements to redirect enemy attacks.
- Fourth Style: Rising Dust Storm (
肆ノ 型 昇 上 砂 塵 嵐?, Shi no kata: Shōjō sa jinran) - Sanemi sweeps his sword horizontally and create multiple cyclone of slashes to deflect enemy attacks.
- Fifth Style: Winter Gale (
伍ノ 型 木 枯らし 颪Go no kata: Kogarashi oroshi?) - Sanemi strikes from above while falling in a multitude of arced slashes.
- Sixth Style: Black Wind Mountain Mist (
陸ノ 型 黒 風 烟 嵐Roku no kata: Kokufū Enran?) - Sanemi unleashes a powerful vertical side way slash upwards at his target.
- Seventh Style: Gale - Sudden Gusts (
漆ノ 型 頸 風・ 天 狗 風Shichi no kata: Keifū - Tengu kaze?) - Sanemi leaps into the air while swinging his blade which generates gale-force winds to shred his opponent apart.
- Eighth Style: Primary Gale Slash (
捌ノ 型 初 烈 風 斬り Hachi no kata: Sho rekkaza kiri?) - Sanemi leaps into the air and swings his blade which generates circular torrents of wind.
- In the first character popularity poll, Sanemi ranked 15th with 207 votes.
- As revealed during his bout against Giyu, Sanemi loves ohagi, and he frequently cooks it. However his pride refuses him from saying anything about it.
- Like Kiyoshi, Sanemi is a marechi, and his blood is considered even rarer for a marechi as it can intoxicate demons and disrupt their senses and movement speed.
- Sanemi always keeps his uniform open, as he is proud of his muscles.
- Sanemi owns a Japanese Rhinoceros Beetle.
- Sanemi lost his right index finger and right middle finger in the battle against Kokushibo. 
- (To Genya Shinazugawa) "You should've gotten married, had some goddamn kids, and lived until you became a goddamn old geezer. For all the times we couldn't do a thing for mom, and for all the times we couldn't do a thing for our little siblings, you should've made your goddamn wife and kids happy as they would have been. Because I would've made sure that no demon would be heading your way..."