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 that Denji saved by giving the wounded demon some of his blood to heal, unintentionally forming a contract with the demon. When the Yakuza betrays Denji and sacrifices him to their master 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.

After he meets Makima, and she forces him to join the Public Safety Devil Hunters and threatens to exterminate him like 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, Makina tells him that if he can manage to kill the Gun Devil she'll 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 them 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.

Katana Man arc
Denji and his team are ambushed by the Katana Man and Sawatari. 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.

Bomb Girl arc
While out on patrol, Denji escapes from the rain in a nearby phone booth, followed by a girl named Reze who is also taking refuge from the rain. After a short conversation, Reze invites him to the cafe that she works at, and gives him a cup of coffee. Because of this, Denji starts to develop feelings for her, as he begins regularly visiting her at the cafe. Eventually, Reze learns through their conversations that Denji has never attended schools, and offers to break into a local school with him. After this, Reze invites Denji to a local festival, and she kisses him during the fireworks display. During the kiss, she bites his tongue off and reveals that she is a Bomb Devil hybrid, after which Beam rescues him and the two make their escape to the Second Division headquarters.

Pursued by Reze, Denji and Beam are assisted by the Second Division for a short time, but are ultimately forced out by her attacks. As the two are chased by Reze, they encounter the Typhoon Devil. After a lengthy battle, Denji ultimately ends up atop a building overlooking the ocean, facing Reze. He uses his chains to grab her, thinking that she won't be able to use her powers underwater, and jumps into the ocean, carrying her with him. Later, the two wake up on the beach, rescued by a now-unconscious Beam. After a short conversation, Denji asks Reze if her feelings for him were genuine. She rejects him, and turns down his offer to run away before leaving. Denji lets her leave, telling her that he'll be waiting for her at the cafe at noon.

International Assassins arc
Within this arc, assassins all worldwide are after Chainsaw Man and his heart, hunting him down. He and Special Division 4 and the rest of their allies are left to defend off these assassins from taking Denji's heart.

Gun Devil arc
During this arc Special Division 4 and a few other divisions are told about the Gun Devils truth and what is truly about to occur on their mission until they are interrupted with the president of the U.S signing a contract with the Gun devil to kill Makima causing Terror across Japans citizens in damages.

Control Devil arc
Within the Control Devil Arc Makima shows her true colors as she leads to the death of his team crushing the people he loves, leading to her eventual death along with the death of Special Division 4's members not including Denji and Kobeni.

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 him of his claims of being Chainsaw Man. Denji later battles and beats Devil Yuko in a one sided fight.

Current arc
Denji goes on a date with Asa on an aquarium, unaware of Asa's plan to turn him to a weapon. The Eternity Devil returns from hell and traps them 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.