"Assassination Classroom the Movie: 365 Days' Time" serves as a sequel to the original "Assassination Classroom" series, encapsulating the final chapter of the story. The film picks up after the events of the anime, focusing on Class 3-E of Kunugigaoka Junior High, a group of students tasked with assassinating their alien teacher, Koro-sensei, before he destroys Earth. The narrative revisits key moments from the series, framed through the perspective of Nagisa Shiota, one of the students, as he reflects on the past year spent under Koro-sensei's unconventional guidance.

The story alternates between flashbacks and present-day events, highlighting the students' growth and the bonds they formed with Koro-sensei. The flashbacks delve into pivotal episodes, such as the students' initial struggles with their mission, their training to improve their assassination skills, and the emotional challenges they faced as they grew closer to their target. Koro-sensei's unique teaching methods, which blend humor, life lessons, and combat training, are central to these recollections, showcasing his impact on the students' lives.

In the present timeline, the students prepare for their final confrontation with Koro-sensei, grappling with the moral and emotional weight of their mission. The film builds toward the climactic moment when the class must decide whether to fulfill their duty or find another solution. The resolution is bittersweet, emphasizing themes of sacrifice, growth, and the enduring influence of a mentor. Key characters like Nagisa, Karma Akabane, and Kaede Kayano play significant roles in the final act, each contributing to the emotional depth of the story.

The film maintains the series' balance of humor, action, and heartfelt moments, providing closure to the characters' arcs while staying true to the tone of the original work. It serves as a fitting conclusion to the "Assassination Classroom" narrative, offering fans a comprehensive and emotionally resonant finale.