Chainsaw Man is a dark, brutal shonen manga and anime franchise that gleefully deconstructs many shonen conventions in unexpected ways, such as twisting the token female friend into a crude and obnoxious antihero like Power or frequently killing off characters no matter the power or friendship. Protagonist Denji, or Chainsaw Man himself, also subverts shonen power scaling in weird ways.
Denji got a massive glow-up when he died and was reborn as Chainsaw Man with Pochita's help, but oddly, he is nigh-unkillable, which threatened to kill the story's suspense. Readers and viewers only care for the hero when there is a real risk of failure or death for them, but Denji can survive absolutely anything, which nearly ruined Chainsaw Man's story until author Tatsuki Fujimoto switched things up entirely for Denji's character.
Denji Can't Generate Suspense, But His Friends Can
Most shonen protagonists have some form of plot armor since they're the main character and the story cannot proceed without them. Even so, shonen leads like Izuku Midoriya and Tanjiro Kamado still feel vulnerable when fighting powerful enemies, and they may lose fights or experience physical scars. Death truly would be the end for them. Skilled manga authors can make their plot armor invisible and make it feel like these heroes really might die, so it's tense to watch these heroes fight with their human mortality being so fragile. Then there's Denji, who is transparently impossible to kill.
Denji has more than plot armor on his side. Thanks to his devilish powers, he survived actual death at the hands of the zombie devil, with Pochita breathing new life into his body as Chainsaw Man. Then, Denji simply outlasted his other foes with incredible stamina and flesh regeneration, such as his bloody battle of attrition against the eternity devil. Denji can even get dismembered and set on fire and still won't die, so he becomes a vehicle for combat scenes with relatively little suspense.
This almost reached critical mass in Chainsaw Man and could have ruined the story, but author Tatsuki Fujimoto pulled back and made sure to switch gears right before that happened. For one thing, Chainsaw Man generates suspense with its supporting heroes like the popular Himeno and the tsundere Aki Hayakawa, who have no plot armor and limited durability. Chainsaw Man engages and shocks fans when characters like them fight and die, and Denji has to accept that. Most of all, the Chainsaw Man manga introduced a new protagonist, Aka Mitaka, and made her more vulnerable than Denji in multiple ways. Denji's appeal as the main character was nearly expended, so he left the spotlight, taking his thick plot armor and incredible in-universe toughness with him.
Denji Survives Everything, But It's Pointless
Denji's plot armor and his in-universe toughness are too high for a traditional shonen battle manga, and if handled wrong, it could have ruined Chainsaw Man by creating low-suspense fights that Denji cannot lose. This almost did happen in Chainsaw Man, only for the series' subversive nature to step in and fix things, which was evidently the plan all along. In the darkest ways possible, Chainsaw Man saved itself from becoming repetitive with devil fights that Denji is guaranteed to survive.
Most of all, Chainsaw Man mocked Denji by making his incredible power and survivability totally empty and pointless to the point of despair. Denji wins nearly all his fights and is too tough to kill, but he has very little to actually live for. He keeps losing his friends and allies, and he is still a lonely, unfulfilled teenage boy who can't get anything he wants, no matter how small and relatable his dreams are. It's almost like a curse, with fate keeping Denji alive with plot armor and devil toughness, but he gets nothing for it, and he's slowly dying on the inside.
In that way, Denji is like One-Punch Man's Saitama, being the #1 fighter on the outside while losing the internal battle for happiness and having a purpose in life. That's what makes Denji truly tragic, though it also gives him a meaningful goal to chase after, and there's plenty of suspense since Denji's outrageous toughness can't help him with this intangible fight. On the inside, Denji is a total underdog with everything to gain, and there's no guarantee of anything. That's why Denji is a true shonen subversion, and it's why he passed the torch to Asa Mitaka so he can restore Chainsaw Man's much-needed suspense while facing his own struggles in the background.