Denji is a teenage boy living in a world where devils are born from human fears, the most powerful among them representing existential terrors like darkness, war, and control. Crushing under a massive debt inherited from his father, Denji survives by hunting weaker devils alongside his only companion, Pochita, a dog-like creature who is also the Chainsaw Devil. After being betrayed by the yakuza and left for dead, a desperate contract with Pochita saves his life: in exchange for seeing his friend's dreams fulfilled, Denji's body merges with Pochita's heart, allowing him to transform into Chainsaw Man, a hybrid being with blades sprouting from his arms and head.

Denji is quickly recruited into Public Safety, a government agency of Devil Hunters, under the enigmatic and powerful Makima. She offers him a simple deal in exchange for his obedience: a life of comfort, regular meals, and a chance to pursue his simple, often crude dreams. He is assigned to a squad alongside the stern and vengeful Aki Hayakawa, who has a personal vendetta against the Gun Devil, and the chaotic, selfish Blood Fiend known as Power. The first part of the compilation follows Denji as he learns to operate within the squad, facing threats like the ruthless Bat Devil and the sadistic Leech Devil, while struggling to understand his new abilities and the moral compromises of his job.

The second part of the compilation shifts focus to a deadly mission inside an endless hotel controlled by the Eternity Devil. Trapped on a single floor with his colleagues, including the experienced hunter Himeno, Denji’s bizarre fighting style and reckless endurance become the squad's only hope for survival. This victory leads to a brief moment of respite, but the celebration is cut short by a coordinated attack from the Gun Devil's human followers. This assault introduces Katana Man, a hybrid like Denji, who decimates their ranks in a brutal confrontation.

The compilation culminates in the full-scale battle against Katana Man and his allies. As the violence escalates, Denji is pushed to his limits, forced to confront the meaning of loyalty and the harsh reality of loss within his new family. The films recaps the events of the first season, ending on a note of uneasy victory and setting the stage for future conflicts, including the looming threat of the Gun Devil and the mysterious true nature of Makima's control. In addition to the main storyline, the compilation includes Chainsaw Days, a series of lighter, comedic vignettes that adapt the manga's bonus chapters, offering a glimpse into the bizarre daily lives and relationships of Denji, Aki, Power, and Himeno outside of their life-or-death missions.