Denji/History

Intro arc
At the start of the series, Denji is forced to do odd jobs and kill Devils for the yakuza to pay off the debt from his late mother's medical expenses that his father didn't pay off before taking his own life. His best friend is a Devil dog named Pochita, whom Denji saved by giving the wounded demon some of his blood to heal, unintentionally forming a contract with him. When the yakuza betrays Denji and sacrifices him to the Zombie Devil, Pochita becomes Denji's heart and revives him as the Chainsaw Devil. Denji then defeats the Zombie Devil and a portion of his zombie army.

Afterward, he meets Makima, who forces him to join the Public Safety Devil Hunters and threatens to exterminate him as a Devil if he ever refuses her orders. After killing the Muscle Devil, Denji becomes a sanctioned Devil Hunter and begins working with Aki Hayakawa and the fiend Power.

Bat Devil arc
The three end up defeating the Bat Devil and Leech Devil, and Power lets Denji get to second base as a reward for saving her cat.

As Denji's joy from the experience slowly turns into melancholy, Makima tells him that if he can manage to kill the Gun Devil, she will grant any wish for him. To find the Gun Devil, the Public Safety Division has to collect pieces of the Gun Devil's flesh granted to other Devils.

Eternity Devil arc
To this end, Denji kills the Eternity Devil after it traps him and Special Division 4 in a moment of time.

During the victory celebration, fellow Devil Hunter Himeno comes onto Denji before throwing up in his mouth during his first kiss and then offers to sleep with him. Denji refuses, wanting to save himself for Makima, and he and Himeno become friends afterward.

Katana Man arc
Denji and his team get ambushed by the Katana Man and Akane Sawatari, and Himeno is killed. Denji is defeated by the pair and only manages to avoid capture thanks to the combined efforts of Makima and fellow Devil Hunter Kobeni Higashiyama.

The strongest Devil Hunter in the Public Safety organization, Master Kishibe, then trains Denji and Power in preparation for an attack on the group that attacked the Public Safety Devil Hunters. Denji has his rematch with Katana Man and wins. Joined by Aki, Denji holds a nut-kicking tournament to see who can get Katana Man to scream the loudest as payback for Himeno.

Bomb Girl arc
While out on patrol, Denji escapes from the rain in a nearby phone booth, followed by a girl named Reze, who also takes refuge from the rain. After a short conversation, Reze invites him to the café where she works and gives him a cup of coffee. Denji starts to develop feelings for Reze and begins visiting the café regularly. Through their conversations, Reze that Denji has never attended school and offers to break into a local school with him. Afterward, Reze invites Denji to a local festival, and they share a kiss during the fireworks display. During the kiss, she bites his tongue off and reveals that she is a Bomb Devil hybrid, after which the Shark Fiend Beam rescues him, and the two make their escape to the Second Division headquarters.

Denji and Beam are assisted by the Second Division for a short time but are ultimately forced out by Reze's attacks. The Typhoon Devil joins the fray, and after a lengthy battle, Denji defeats Reze, using his chains to restrain her. Thinking she will not be able to use her powers underwater, he throws themselves into the ocean. Later, the two wake up on the beach, rescued by a now-unconscious Beam. After a short conversation, Denji asks Reze to run away with him and if her feelings for him were genuine. She rejects him and turns down his offer to run away. Denji lets her leave but tells her he will be waiting for her at the café at noon. With a backpack and an envelope of money, Denji waits at the café with a bouquet for Reze, but she never comes.

International Assassins arc
The fight with Reze has revealed Chainsaw Man to the world, and assassins from around the globe hunt down Denji and his heart. Together with Devil Hunters from Public Safety, Special Division 4 works to protect Denji from his assassins, one of them including Quanxi, the First Devil Hunter, and the Crossbow Devil hybrid. During the all-out battle, the Hunters get sent to Hell and encounter the Darkness Devil. Denji attempts to fight the Devil but is quickly incapacitated. They are rescued by Makima, who revitalizes Denji and has him defeat Santa Claus.

Gun Devil arc
Special Division 4 recovers from their encounter in Hell, with Aki and Denji taking care of a now-traumatized Power. Makima invites Denji to go on a trip with just the two of them, but he turns her down to help Power. During this time, Denji concludes that there are some things he is better off not knowing. Afterward, Special Division 4 learn the truth about the Gun Devil from Makima and that they are to take a piece of its body from another country into Japan's possession. When the Gun Devil attacks Japan to kill Makima as ordered by the U.S., Denji and Power are attacked at home by Aki, who has transformed into the Gun Fiend. With no other choice but to stop him by the pleas of the innocents, Denji kills Aki, which greatly disturbs him.

Control Devil arc
With Denji at his lowest, Makima shows her true colors as the Control Devil, killing Power and revealing her true intentions with Denji: to break his contract with Pochita and gain access to Chainsaw Man and his ability. Makima proceeds to break Denji's psyche, leaving him in a catatonic state. Pochita takes control of his body and tries to restore their contract. With the help of Power, Denji is brought back and hides away with Kishibe and Kobeni. Watching the television showing the positive reception to Chainsaw Man, Denji expresses his selfish dreams for his life and desire to keep being Chainsaw Man. Plotting with Kishibe, Denji confronts Makima for the final time, leading to her eventual defeat. Despite everything Makima did to him, Denji still likes her, and to stop her from reviving, he commits to cannibalism and eats Makima's body.

Denji meets with Kishibe, who puts Nayuta, the reincarnated Control Devil, under his care. Denji has a dream with Pochita, who tells him to grant the Control Devil's dream by forming an equal relationship with her as a family. Denji then leaves Public Safety and starts attending high school while continuing to be Chainsaw Man.

Justice Devil arc
Battling the Cockroach Devil, Denji inadvertently saves Asa Mitaka and Yuko, once again killing the Bat Devil in the process. Killing the Cockroach Devil, he is acclaimed by the news for saving a cat. Still wishing to get a girlfriend, he made several attempts to expose his identity, but to no avail Hirofumi Yoshida protects his identity under a secret mission. He later meets Asa, who rejects his claims of being Chainsaw Man. Denji later battles and beats Devil Yuko in a one-sided fight.

Dating Denji arc
Denji gets invited on a date with Asa to the aquarium, unaware of her plan to turn him into a weapon. The Eternity Devil returns from Hell and traps both of them along with several members of the Devil Hunter's club via Fami's scheme to turn him into a weapon, having Denji to face it again with Asa.

While trying to find a way out, Denji tells Asa more about himself, and the two bond as she devises an escape plan. After gathering over one million yen, Asa tells Denji to give her the money, promising to grant any request after they escape, and Denji agrees. Everyone is freed from the aquarium after Asa changes it to a spear, while Denji is simply happy to touch a penguin. Denji walks Asa home and asks her on a second date, which she agrees to do. Suddenly, Yoru possesses Asa, puts her hand on Denji's head, and calls out: "Denji Spinal Cord Sword." Denji is confused and interprets this as a farewell, mimicking her before leaving. The next day, Denji meets up with Asa after school and tells her his date plan: watching a non-stop movie marathon at the theater. Asa complains about the price, and they agree to have the movie date at Denji's home. Denji reluctantly accepts under the condition that Asa follows the home's rules because, in the worst-case scenario, she could die if she breaks them.

Denji takes Asa to his apartment, where he explains the home's rules to her. As they watch the movie together, Denji tells Asa not to make out with him in front of his roommate, which gets Asa flustered, and she says she has no desire to kiss him and actually hates him. She then says that Denji should stay away from her and she only went on a date with him for a distraction. Denji is shocked and wonders what he did wrong. Looking back to a past statement made towards him, Denji assumes that Asa hates him because he smells like a dog. He turns to ask Asa if she thinks dogs smell but is met by Yoru, who kisses him. Suddenly, the door bursts open with Nayuta and the other dogs on the other side. Nayuta sees the two and points at Yoru, calling her a thief. After she says this, a chain emerges from her finger and links through Yoru's skull.

Nayuta turns Yoru into a dog and makes her bark, to her amusement. Denji tells Nayuta to turn "Asa" back immediately, which they both agree to do after she finishes his cooking. While she eats, Nayuta asks Denji if he is sure he wants to turn "Asa" back, reminding him that every woman he meets tries to kill him and asks what makes her any different. After some thought, Denji states that it is a feeling. Nayuta agrees to turn back the girl but on two conditions: allow her to eat ice cream every day and not make friends with Asa anymore. A shocked Denji asks why, and Nayuta answers that "Asa" has a bad scent, then proceeds to say she will alter her memories to make her believe that Denji stood her up. Denji is conflicted but decides to put Nayuta first.

Current arc
At night, Nayuta smells a "nasty devil scent" and insists that Denji go hunt it. However, Denji is depressed and does not want to be Chainsaw Man anymore, saying that Nayuta will only block him from more future ladies. Nayuta tells Denji that if he turns into Chainsaw Man, he could get more love from people than a girlfriend. After some thought, Denji quickly regains motivation.