Pochita

Pochita, also known as the Chainsaw Devil, is a Devil that embodies the fear of chainsaws and acts as the heart of Denji, giving him the power to transform into Chainsaw Man.

Being regarded as the Devil that Devils fear the most, the Chainsaw Devil is considered one the most powerful entities in the series after the Primordial Devils, being able to fend off hordes of Devils in Hell unscathed. The hunt for his heart alone was enough to cause an international conflict, and even Makima, one of the Four Horsemen, considered herself inferior to him, needing the public's adoration to weaken and defeat him.

As of becoming Denji's heart, he is able to speak with him telepathically, and gives him the power to go chainsaw when the ripcord in his chest is pulled.

Physical Appearance
After disappearing from his battle with the Four Horsemen and Weapon Devils, Pochita is reduced to a “near-death state”. In this state, he appears to be a small orange canine-like Devil with a chainsaw-like appendage protruding from the center of his head. Handles emerge from his body allowing him to be wielded like a chainsaw, and his short tail is in the shape of a chainsaw's pull cord.

Occasional Appearances
His true Devil form is of a large, humanoid Devil with four arms and a chainsaw protruding from each, with another chainsaw coming from the front of his head, similar to Denji's hybrid form. An intestine still connected to his stomach is wrapped around his neck, resembling a scarf or a collar.

After making a contract with Denji, Pochita assimilates himself with him, fusing with his heart and becoming part of Denji's anatomy, thus creating a hybrid. This allows Denji to become Chainsaw Man by pulling the chainsaw cord in his chest. In this state, Pochita is smaller, has lost the chainsaw on his head, all his appendages and both handles. Pochita also has blood vessels connected to Denji. Pochita however still retains his trademark cute canine face. Denji's chainsaw cord is also directly connected to the top of Pochita's head.

After transforming into Denji's heart, his form is literally attached to Denji.

He is also seen inside of Denji's body literally as the heart, with eyes and a mouth.

Hybrid Powers

 * Hybrid Transformation: By pulling on the cord emerging from his chest, Denji can transform into a bloodthirsty Chainsaw Devil. Denji needs blood in order to use his abilities, so if he does not have enough of it in his body, he can not fully transform and will instead enter a pseudo-hybrid form.
 * Augmented Strength: After entering his Hybrid form, Denji's physical strength is increased exponentially.
 * Chainsaw Manifestation: As part of his transformation Denji grows fully-functional chainsaws from his arms, legs, feet and head.
 * Devil Transformation: After surrendering his contract with Pochita, Denji transformed into a Full Devil. In this form, Pochita displays incredible speed and strength, easily defeating multiple Hybrid Devils in a matter of seconds.
 * Blood Consumption: Denji is able to heal completely from nearly any fatal injury, and in some instances recover from death, so long as he consumes a sufficient amount of blood. After losing his arm to Bat Devil, Denji's arm re-attached itself after he received a blood transfusion.
 * Nigh-Immortality: Due to being a Hybrid, Denji is immortal and nearly unkillable. He can survive getting shot, being thrown from buildings and taking all kinds of injuries that would kill most Devils. Even if he dies, as long as someone pulls the cord on his chest, Denji can come back to life in perfect condition.

Devil Contracts

 * Chainsaw Devil Contract: In exchange for living a "normal life", Pochita became Denji's heart and turned him into a Hybrid. All of his Hybrid abilities are originated from this contract.
 * Blood Devil Contract: In exchange for finding reincarnated Blood Devil and befriending with them, Power gave all of her blood to revive Denji.
 * Blood Chainsaw: Thanks to blood gained from Power, Denji is able to manifest a chainsaw from her blood. It has similar design of Power's horns. By using her blood manipulation ability, Denji is able to disturb regeneration of Makima which allowed him to defeat her.

Part 2: Academy Saga

 * Chapter 36: Ordinary Happiness (mentioned)
 * Chapter 42: A Chair's Feelings (mentioned)
 * Chapter 53: Dream's Next Stage (vision)