"Eiga no Osomatsu-san" is a feature-length anime film based on the popular comedy series "Osomatsu-san," which itself is a modern revival of the classic 1960s manga and anime "Osomatsu-kun." The film retains the absurdist humor and chaotic energy of the series while expanding its scope into a cinematic format. The narrative centers on the Matsuno sextuplets—Osomatsu, Karamatsu, Choromatsu, Ichimatsu, Jyushimatsu, and Todomatsu—who are perpetually unemployed, lazy, and prone to causing trouble. Despite their identical appearances, each brother has a distinct personality, which drives much of the film's comedic and dramatic tension.

The story begins with the brothers living their usual aimless lives, engaging in petty schemes and squabbles. However, their mundane existence is disrupted when they encounter a mysterious figure who offers them a chance to change their lives. This encounter leads to a series of bizarre and surreal events, including time travel, alternate realities, and encounters with exaggerated versions of themselves. The film explores themes of self-reflection, identity, and the consequences of their actions, as the brothers are forced to confront their flaws and the impact they have on those around them.

Throughout the film, the Matsuno brothers interact with a variety of recurring characters from the series, including their childhood friend Totoko, the long-suffering Iyami, and the eccentric Chibita. These interactions often escalate into absurd and over-the-top scenarios, blending slapstick comedy with moments of unexpected poignancy. The film's narrative structure is non-linear, with frequent shifts in tone and setting, reflecting the chaotic nature of the brothers' lives.

The climax of the film involves a high-stakes situation that forces the brothers to work together, despite their constant bickering and selfish tendencies. This resolution highlights their underlying bond as siblings, even as they continue to struggle with their individual shortcomings. The film concludes with a return to their usual antics, suggesting that while they may have grown somewhat, their core personalities remain unchanged.

"Eiga no Osomatsu-san" successfully translates the series' signature humor and character dynamics into a feature-length format, offering both longtime fans and newcomers a chaotic yet heartfelt experience. The film's exploration of the Matsuno brothers' relationships and its blend of comedy and introspection make it a standout entry in the franchise.