Kokushibo was an extraordinarily powerful demon, proven to be the strongest of the Twelve Kizuki and the second strongest demon in the series, just behind Muzan Kibutsuji. As one of the oldest demons in the series, he had battled numerous Demon Slayers and obtained vast experience and knowledge of combat. He was able to easily decipher the techniques and skills of at least two Hashira and overwhelm them in battle. As a Breath Style user, he possessed tremendous levels of strength and reflexes that were further enhanced by his demon physiology.

Enhanced Vision: As Kokushibo possesses 3 pairs of eyes, his eyesight has not only been augmented physically, but supernaturally as well, granting him superhuman kinetic vision similar to Kanao Tsuyuri that make the world seem to move in slow-motion in addition to predicting opponents' attacks and movements by observing the subtle shifts of their muscles, joints and the slight movements of their eyes, which is further enhanced by his access to the Transparent World through this same superhuman vision.

Extrasensory Perception: Kokushibo can detect presences of others outside of his range of perception, as shown when he dodged Genya Shinazugawa's gunshots and appeared directly behind him despite Kokushibo not looking at Genya at all. With the Transparent World, he could perceive the bodily structures and see through the bodies' of his opponents and use this information to predict their attacks and movements. He also seems be extremely proficient in the use of the Transparent World, being able to trace back the heritage of a young child back to his own bloodline with a simple glance.[14] He's also able to immediately determine how strong his opponents are by looking at their muscles and bodily structure.[15] Outside of his vision, Kokushibo also seems to be able to keep track of the locations of his peers around the Infinity Castle, evident as he no longer felt Akaza's presence when he died.[16]This grants him immense reaction and reflex speeds and allow him to perceive multiple attacks from different directions seemingly outside his line of sight[12], and to see from long distances.

Flesh Manipulation: Like all Demons, Kokushibo possesses the ability to manipulate his own flesh, although at a much higher caliber since he assimilated a lot of Muzan's blood. He used this ability to grant himself multiple eyes that augment his vision to supernatural levels. He has also used this ability to create an extremely durable and sharp katana, complete with a handguard and scabbard. Because of this, his katana can never be destroyed as he can regenerate it like he would with normal wounds.

• Sword Manipulation: As an extension of his flesh manipulation ability, Kokushibo can manipulate a detached part of his body in the form of his katana.[17] This allows him to easily regenerate parts of if it was destroyed or damaged as he would his body, which was shown numerous times when the blade returns to its original shape when Gyomei Himejima or Sanemi Shinazugawa damaged it with their attacks. Furthermore, he can freely manipulate the form of the blade, shown when he grew three additional blades from the original blade to increase its reach and further increase its size. While engaging in combat, he can manipulate the length and size of his sword strikes, allowing him to cover a distance normally unachievable by a human swordsman. Later, Kokushibo also displayed the ability to grow and protrude multiple blades from his own body, allowing him to perform a multitude of slashes from them without a swinging motion. This attack was powerful enough to easily blow away two Hashira and destroy Genya's Blood Demon Art, as well as slice in half numerous columns in the room, from just its activation.

• Demonic Transformation: Later, upon re-growing his head while battling Gyomei and Sanemi, Kokushibo was able to transform himself into a more monstrous form with several appendages on his back that enhanced all of his abilities and powers to presumably the same level as the Demon King, Muzan Kibutsuji.[18]

Haha there's more

Immense Speed & Reflexes

Immense Regeneration

Immense Strength

Indomitable Will

Tactical Intellect

Unlimited Stamina & Endurance

Immense Durability

Above info all from the KNY fandom, plus he utilized a breathing style second only to the most powerful sun breathing, which has sixteen stupendous forms. Breathing styles are swordmanship styles which for me, makes slicing off a demon's head more magnificent and efficient.

Stronger feats and a good bit faster . Demon takes it high diff

Kokushibo could slice him within seconds. That too using the first breathing technique itself imo

Disagree. They arent that far apart honestly. Demon has to avoid all that ice and shit he cant blitz him.

Well his sword reflexes are intensely fast. Slicing through the barriers would be no sweat, with his perception and vision as the main perks. He would face Unalaq in close combat then.

Unalaq can rebuild ten he's not just gonna be sitting there waiting to get sliced. In the end demon wins but it's no gonna be a walk in the park.