The following contains spoilers for Episode 1 of Chainsaw Man, "DOG & CHAINSAW," now streaming on Crunchyroll.
The hit Fall 2022 anime Chainsaw Man, based on author Tatsuki Fujimoto's ongoing manga series of the same name, stars a shonen protagonist who differs from his peers. Unlike Izuku Midoriya and Tanjiro Kamado, Denji lacks a major villain to defeat; he isn't idealistic, noble or selfless either. He grows meaner in his adventures, not nicer.
All this firmly establishes Chainsaw Man's protagonist as a classic antihero, a protagonist whose motives, methods and worldview make them exciting to watch, but neither relatable nor inspiring. The same can be said about Attack on Titan's Eren Yeager after a point, with both Eren and Denji dying only to be reborn as true monsters with terrifying powers.
When the Antihero Is Reborn for Nothing But Battle
It is rare for an anime hero to outright die in a series, especially early on. Even suspending disbelief, viewers know deep down that the hero has pretty thick armor because the story can't happen without them, so some series try to build tension with fake-out deaths. Then there are truly brutal or experimental series such as Chainsaw Man and Attack on Titan that really do kill off their heroes -- or at least do a great job with a fake-out. Denji didn't just lose his first fight against the zombie devil; he was outright killed, and his chopped-up body was stashed in a Dumpster along with Pochita the chainsaw devil dog. Similarly, Attack on Titan fans watched Eren lose two limbs before a bearded pure Titan ate him, and fans actually thought Eren was dead, given all the deaths going on in that sequence.
Then Denji and Eren were reborn -- sometimes literally -- with new powers and a new purpose. When Eren learned that he wielded the Attack Titan, his life was forever changed and he embraced his new role as Paradis Island's ultimate living weapon. Even in the context of his hometown's destruction, Eren's life had undergone a radical shift, and there was no going back. His old life was gone, putting Eren on the path to becoming an Eldian restorationist radical and a collector of Titan Shifter powers to make his world-shaking dreams a reality.
Denji doesn't aim to change the world in Chainsaw Man, but he does know what it's like to be reborn for a singular purpose, with his old life forever wiped away. He was an outcast even before his transformation, but now he truly has no place in human society. As a half-devil, Denji is a man of no worlds at all, having nothing but his enemies and his own powers to define his violent new lifestyle. Like Eren, Denji has been reborn for the sole purpose of war, and as Episode 1 showed, he is gladly embracing this radical change. He had extremely little to lose and now has plenty to gain as Chainsaw Man. Eren would say the same about his Attack Titan form.
How Attack on Titan's Eren & Chainsaw Man's Denji Twist Shonen Protagonist Tropes
Compared to the "big three" shonen series' heroes and more modern leads such as Midoriya, Tanjiro, Yujia and even Anya Forger, Eren Yeager and Denji are both total antiheroes who shred the shonen protagonist rulebook without a second thought. They were reborn as deadly warriors with a single purpose, abandoning their miserable past lives to embrace a lifestyle of violence and self-centered motives -- but as they are products of their environments, they go about it differently.
Sheer survival is the name of the game in Attack on Titan, with the walled city's defenders fighting desperately to not be eaten and Eren launching his campaign to ensure the Eldians' survival in a world that wants them dead. Shonen heroes usually fight for loftier ideals such as justice, peace, the law and general goodness; for them, survival is only a means of lasting long enough to get the real job done. Eren, however, thinks more like a beast listening to its own instincts, fighting anyone and anything that threatens its existence.
Chainsaw Man's Denji, meanwhile, also has sheer survival on his mind; he fights not to enforce justice or defeat evil, but to get three meals a day and a roof over his head. On a personal level, Denji hopes to get a girlfriend, a fairly wholesome and innocent desire to have, but overall he still lacks the idealism that is essential for most shonen leads. In fact, Denji never really had any idealism at all, since his transformation into Chainsaw Man only boosted his combat power and freed him of his debt.
Denji is the same humble, self-absorbed punk he always was, except he was reborn with chainsaw devil powers. This transformation was a purely physical one, with his reborn body merely allowing him to fight that much harder for his simple goals while ignoring idealism entirely. In that way, Denji is a true antihero, refusing to use his new gifts for the good of others or society. He just wants lunch.