Hybrid

Hybrids, also referred to as a devil-human (real name unknown) are humans who have merged with and can take on the form of a Devil.

Overview
The official name for hybrids was eaten and erased by the Chainsaw Devil, but hybrids continue to exist despite their erasure for unknown reasons.

In rare cases, a human can become fused with a devil and turn into a hybrid. The only known method of becoming a hybrid is via a contract or surgery, in which the devil replaces the human's heart. The hybrid's heart therefore becomes both their source of power and weakness.

Hybrids keep their human consciousness and appearance but can transform into human-devil hybrids through a trigger and manifest the supernatural abilities of their fused devils. When transformed, the head and, in many cases, the arms are affected, while the rest of the body remains human. Though their appearance varies from weapon to weapon, most of them take on a mechanic/metallic appearance and all of them lack lips, exposing monstrous teeth. When they are not transformed into devils, they are, with the exception of their triggers, indistinguishable from regular humans, unlike fiends.

Although the human is fully in control when transformed, the devil inside them can also take control and turn back to their devil form if their contract is broken, as seen when Pochita took over Denji's body and fully transformed into the Chainsaw Devil. The devil is also able to reform into their original selves if the hybrid tears out their heart, though this would presumably leave the human unable to transform.

Currently there are eight known hybrids: Chainsaw, Katana, Bomb, Crossbow, "Spear", "Flamethrower", "Longsword", and "Whip". Besides Chainsaw, the others are collectively named as Weapon Humans and were members of Special Division 5 under the supervision of Makima.

Their triggers are all based on the weapons whose fears their powers are based on and manifest on various spots on their bodies. The chainsaw hybrid has a chainsaw cord on his chest, the bomb hybrid a grenade pin on her neck, the crossbow hybrid an arrow in her right eye socket. The spear hybrid has a spear he can pull out of his neck. The katana and longsword/broadsword hybrid have their respective weapon manifested in their arms. Unlike the rest, the whip and flamethrower hybrid trigger their transformations by making certain motions with their hands.

There is a similar phenomenon called devil transformations which, like hybrids, is a human who can take on the form of a Devil as a result of a contract. The main difference being that there is no merging between a human and devil for this scenario and that people with a devil transformation appear to become full on devils, and might need help to turn back into humans from an outside source, while hybrids are considered to be neither devil, human or fiend and can freely transform. They are also visually different in that all seen devil transformations have been more monstrous while hybrids retain a human shape with only a demonic appearance in the head area and arms.

Abilities

 * Hybrid Transformation: The main ability of a hybrid is transformation into their respective devil forms fused with their human form. Certain actions act as triggers for hybrid transformation, with each action usually referencing a part of the devil a human is fused with (Ex. Denji transforms by pulling Pochita's tail like a Chainsaw start cord, Reze takes out a pin in her neck like a pin in a grenade). Their strength, speed, and durability are increased dramatically after the transformation and they also gain the ability of their respective Devil. Their transformation usually affects their heads and arms, but skilled hybrids can also transform their legs into weapons.
 * Immortality: Although hybrids can regenerate by drinking blood just like devils and fiends, they are also able to regenerate and even recover from fatal injuries by activating their trigger without needing to drink blood. Examples of this ability include when Denji split Katana Man in half, but the halves stuck themselves back together when Denji activated Katana Man's trigger by pulling off his left hand, or the numerous times Denji has been revived by having his cord pulled. This makes hybrids immortal, as unlike devils and fiends who go to Hell when they die, hybrids will remain on Earth for seemingly unlimited time. This is exemplified by Makima bringing back Reze and Quanxi, long after they seemingly died.


 * Blood Consumption: They are able to restore their health by consuming blood, like devils and fiends. Moreover, their regenerative abilities are limitless and they can revive if there is an adequate amount of blood to consume, even if their head is severed or their heart is removed from their body. If there is not enough blood, the transformation will stop on the way even if they try to transform again, the armament will not appear even if you perform certain actions, or only the damage will recover and return to the human form. When transforming or disarming, the changed parts melt like mud.


 * Contract Creation: Like regular humans, and unlike fiends, hybrids can make contracts with devils, as it is shown that despite having a contract with Pochita, Denji is also able to contract with the Blood Devil. However, it is unknown if the devil inside the hybrids can make a contract with other humans.

Trivia

 * The term "hybrid" is a widely accepted placeholder name among fans but they are more accurately described as being fusions/merges between an already existing human and devil than a crossbred hybrid. While a hybrid doesn't necessarily have to refer to beings born through interbreeding means only, the term is most often used, in real life and in fiction, to refer to such. A devil and human hybrid is a term often used in other media to refer to the offspring born from a devil and human and not some transformation or fusion later in life, but there are exceptions.
 * In Chapter 103 a news reporter refers to the Chainsaw Man as a "devil-human" which sounds similar to one of the translations for the alternate translation for fiends "Devilman" or Devilmen. While this is one of the most "official" names in reference to the kind that we can get it still should not be taken as canon as the name is unrevealed and no one remembers it.
 * While all the hybrids currently seen are only weapon based, it is unknown if only weapon devils can become a hybrid or not.
 * It would also be doubly questionable as to what would qualify as a weapon or not, as many things can be used as a weapon but have other uses and vice versa, such as how chainsaws themselves weren’t originally weapons but were made for medical purposes.
 * It's possible that hybrids stop aging. Quanxi is known as the "first devil hunter" and used to be Kishibe's teammate when he was young. Unlike Kishibe, who has noticeably aged, Quanxi still looks the same.
 * Outside of Chainsaw, Katana, and Bomb, the majority of the hybrids don't have a fully canon name for their weapons, causing some inconsistencies in which to exactly name some of them (such as if the western sword is either Longsword or Broadsword). Until they get proper canonized names for their exact weapon types, they often get referred to what they can just be called visually.
 * Other devils who have consumed or tasted hybrids, like the Bat Devil and Fox Devil for example, say they taste bad.