"Bungo Stray Dogs: Dead Apple" is a feature-length anime film set in the universe of the "Bungo Stray Dogs" series. The story unfolds in a world where individuals possess supernatural abilities tied to literary figures, known as "Ability Users." The narrative centers on a mysterious phenomenon in which Ability Users are found dead, their abilities seemingly having turned against them. The incidents are linked to a fog that envelops the city, isolating it and trapping its inhabitants.

The Armed Detective Agency, a group of Ability Users who solve supernatural cases, investigates the crisis. Atsushi Nakajima, a new member with the ability to transform into a white tiger, takes a central role alongside his mentor, Osamu Dazai, whose ability nullifies other powers. The agency discovers that the fog is connected to Tatsuhiko Shibusawa, a dangerous Ability User with the power to manipulate others' abilities. Shibusawa seeks to create a world where only the strongest Ability Users survive, using the fog to force confrontations between individuals and their own powers.

As the investigation progresses, Atsushi and his allies confront Shibusawa, who has orchestrated the chaos to draw out powerful Ability Users, including Atsushi and Ryunosuke Akutagawa, a rival with a destructive ability. The film explores themes of self-acceptance and the struggle to control one's inner darkness, as Atsushi grapples with his own insecurities and the destructive potential of his ability. The climax involves a high-stakes battle against Shibusawa, who aims to absorb the abilities of others to achieve ultimate power.

The film also delves into the backstory of Dazai, revealing his past connections to Shibusawa and the Port Mafia, a rival organization. This adds depth to the narrative, highlighting the complex relationships between characters and their shared history. The resolution sees Atsushi and his allies overcoming their internal and external conflicts, ultimately defeating Shibusawa and restoring peace to the city.

"Bungo Stray Dogs: Dead Apple" expands on the series' lore, offering a self-contained story that complements the main narrative while introducing new challenges and character dynamics. It maintains the blend of action, mystery, and psychological depth characteristic of the franchise, appealing to both existing fans and newcomers.