Slasher takes the form of a bald middle aged man of a reasonably muscular build with a lime green iris, a black sclera and vertical slits for pupils along with sharp pointed nails that are dark blue in color and several prominent fangs in his mouth. Most prominently, Slasher's whole body is covered in dark blue tattoos, running across various places on his face, limbs and torso. These tattoos light up and glow a lighter blue when he uses his Blood Demon Art. He also wears a sleeveless blue shirt and black leggings complete with tabi socks and a pair of zōri with blue straps. Slasher is usually seen with a maniacal expression on his face.
Like most of his kind, Slasher is a ruthless demon that only seems to care about murdering and eating humans, He also is shown having a sadistic and malicious nature, off-handedly mentioning he slashed a woman till he became bored and digging his claws into a young boy. He is also shown to be quite arrogant at times, looking down on the Flame Hashira, Kyojuro Rengoku and boasting his speed in front of him as well as challenging him to a duel twice. However, Slasher is also capable of using underhanded tactics like taking a hostage to win against Demon Slayers.
Slasher was also rather petty, trying to find whatever means to provoke Kyojuro and growing further frustrated and more aggressive when the young man both held his ground, retorted back and even stopped his murders.
Slasher began terrorizing a village in search of prey. He found a young woman roaming around at night but thought she didn't seem worth eating. Instead, he decided to horrifically slash her body till he became bored and left her to die. The next night, he boarded a train but found it empty, apart from one hapless train conductor. He quickly killed him but found him not worthy to devour too and left his body to be discovered. The news of his actions frightened the village and people feared leaving their houses after dark, causing business usually active at night to halt. The Demon Slayer Corps. subsequently sent Kyojuro Rengoku to investigate.
Slasher happens upon a maintenance facility for trains in search of prey. Unbeknownst to him, the facility held the Mugen Train, which is assumed to hold a demon likely responsible for numerous disappearances reported. He finds a young worker and grasps him in his claws. The scene draws the attention of Kyojuro, investigating the Mugen Train, and Slasher is confronted by the Hashira. While facing him, he wretches suddenly, before stepping on a bento box, claiming that human food is disgusting to him now as a demon. He taunts Kyojuro into attacking him, using his Blood Demon Art to rush around the Hashira and goad him into attacking, warning him that the young boy will be dead if he directly tried to attack. Kyojuro acknowledges his speed but tells him not to get cocky. Slasher mentions how he injured a woman the previous night but is told by Kyojuro that she will recover completely. Angered, he notices the stepped bento box and Kyojuro's angered expression, before realizing the box likely came from a nearby station. Deciding he will kill the vendors to spite Kyojuro, he first tries to kill the boy he is holding but has both of his hands cut off. He retreats and steps outside the facility to regrow both his hands, before smelling the air for the bento vendors' scent and following the tracks, using his Blood Demon Art to cross the great distance in minutes.
He arrives at the station and enters, seeing the young girl setting up her bento stand. As she staggers in fear of seeing him, Slasher moves forward to kill her but is hit by a bento box from behind, thrown by her grandmother. Momentarily distracted by the smell, he soon catches up to her outside and tries to crush her throat. Kyojuro thwarts his attack and slices his left achilles, saving her. Slasher decide to kill her grandmother instead but is confronted by Kyojuro. Wondering aloud how he manage to catch up to him so quickly, Kyojuro repeats his earlier words not to get cocky facing him. Slasher decided to make a contest for the two to determine who is faster, if Kyojuro can kill him before he kill the girl's grandmother. To this, Kyojuro mocks him for being slow and decapitates Slasher before he is able to react, ending his short spree of terror.
Overall Abilities: Slasher was a decently powerful demon, as evidenced by developing a Blood Demon Art and displaying skill in utilizing it for combat. He also proved mildly troublesome for even a Hashira to handle, albeit most of it attributed to his penchant to use human shields. In direct combat, Slasher proved no match for a Hashira.
Regeneration: Like all demons, Slasher possesses enhanced regeneration. He was able to grow both his hands back in moments after having them cut, as well as healing his sliced achilles just as quickly.
Speed Enhancement: Slasher's Blood Demon Art enables him to greatly augment his own speed, allowing him to traverse great distances in a short amount of time. This technique is activated whenever his dark blue tattoo glows. The speed at which he moves is such that his entire figure is covered in a blue light.