Sanemi is a fierce and skilled Hashira, known for his loud and ruthless demeanor. He has a muscular build, spiky white hair, and large purple eyes. His body is covered in scars from his battles with demons. Despite his harsh exterior, Sanemi has a complex personality and can be surprisingly caring.
Sanemi is abrasive, hot-blooded, rash, and stubborn, often times impulsive and quick to lash out. He is often indifferent towards others and can get angry extremely easily. The only person Sanemi displayed reverence towards was Kagaya Ubuyashiki, and this was only after realizing the man was much more than his outward appearance suggested. Sanemi has also displayed a hunger for battle, wishing that he could encounter Upper Rank demons and proclaiming his excitement in fighting Upper Rank One, Kokushibo.
Sanemi's cold, rude, and dismissive behavior is the result of losing too many people he cared about in the past. Later, when he sees those people who have passed, such as his mother, he can't help but give her a smile to be able to see her again. When Genya joins the Demon Slayers in search of him, Sanemi repeatedly dismisses and lashes out during any chance of seeing 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 them, Sanemi harbors a deep hatred towards demons and is convinced that humans and demons can never coexist. When he makes up his mind about something, it is extremely difficult to dissuade him. He did not believe Tanjiro's insistence that Nezuko Kamado wouldn't eat humans and even moves to prove his own point by stabbing through the box with Nezuko inside.[4] 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.
Tanjiro is ultimately right about Sanemi. Despite his poor treatment of his brother, Genya, Sanemi truly did love and care for his brother, admitting that he blames himself for not protecting him. He even expresses that he wished that Genya would settle down and have a family. Following the battle with Upper Rank One, Sanemi shows not only great anger and a certain emptiness towards Muzan, but more cooperation with the likes of Giyu, someone he clearly did not get along with in the past. Even when Sanemi is launched out of the battle against Muzan, he displays undeniable courage and determination, like his fellow Hashira. When the showdown with Muzan is finally over and time has passed, Sanemi has clearly mellowed out a bit. He is able to smile with Giyu, even after their past confrontations. Most surprisingly, he admits his mistakes and apologizes to Nezuko about his actions. It goes to the point he gives her a smile and a pat on the head, as he sees Genya in the way she responds.
