Tatsuki Fujimoto's Chainsaw Man is no stranger to violence, portraying the harsh reality of living in a world infested with devils. There is a lot of bloodshed and everyday violence involved as Devil Hunters risk their lives fighting these otherworldly creatures.
Denji, our protagonist, constantly faces off against these devils, sustaining life-threatening injuries in the process. He even ended up being cut in half by the Katana Man at one point, technically causing his death. However, unlike other characters, he managed to survive the ordeal and recover. This raises questions among fans as to how he can survive even after being literally cut in half.
Disclaimer: This article contains major spoilers from the Chainsaw Man series.
Denji and his contract with Pochita that makes him immortal in Chainsaw Man
Denji made a pact with the Chainsaw Devil, Pochita, turning him into a hybrid. In Chainsaw Man, hybrids maintain their human features while also being able to transform into a human-devil fusion with the help of a trigger. Denji could turn into Chainsaw Man after fusing with Pochita, who became his heart. Pochita made this sacrifice as he cared deeply for Denji and wanted him to fulfill his dream of living a normal life.
As a hybrid, Denji was able to access the abilities of the Chainsaw Devil, giving him the power to erase any devil from existence by killing them with his chainsaw and devouring them. He also became immortal as he could regenerate from injuries as long as he had access to blood and the required body parts.
The power of regeneration, however, doesn't mean that hybrids don't face danger from mortal injuries. During his fight with Katana Man, Denji got cut in half and was incapacitated with his upper body being taken away. This was done mainly to extract Denji's heart. The hybrid heart is what helped Denji regenerate and if the villains succeeded in removing it, Denji could have officially died.
He survived the attack as Makima and Kobeni assisted him in time, stopping the villains from extracting his heart. Kobeni was the main hero of the event as she protected Denji from Sawatari and Katana Man with the help of her lightning-fast reflexes and stellar combat abilities. She easily dodged the Snake Devil's attack, sliced off Katana Man's arm, and provided suppressing fire at a critical moment.
Kobeni's powerful assault, along with Makima's use of her Control Devil powers, forced Sawatari and Katana Man to flee without taking Denji's upper body with them. This allowed both his body parts to be brought together, helping him regenerate.
Denji has technically died numerous times in the anime for one reason or another. From being killed by Kishibe during training to getting sliced in half by the Katana man, he has sustained life-threatening injuries repeatedly and has managed to survive through his powers of hybrid regeneration.
After fusing with Pochita, Denji also became a target for devils everywhere, with the likes of Gun Devil, Bomb Devil, and Control Devil targeting his heart. His heart was the Chainsaw Devil itself, making it a threat to devils everywhere.
Chainsaw Devil has the power to erase any devil from existence by killing and devouring them. This makes the devils unable to reincarnate, not in hell or in the human world. Their existence is erased from the universe along with the fear of their name being forgotten by humanity. This is why Chainsaw Devil is feared the most by other devils and has been given the moniker of "The Hero of Hell."