"Eiga Oshiri Tantei: Sufūre-to no Himitsu" is a feature-length anime film based on the popular children's book series "Oshiri Tantei" (Butt Detective). The story centers around the titular character, Oshiri Tantei, a detective with a distinctive appearance—his head resembles a human buttocks. Alongside his assistant, Brown, a dog with a penchant for solving puzzles, Oshiri Tantei tackles a series of whimsical and lighthearted mysteries.

The narrative begins with Oshiri Tantei and Brown receiving a mysterious invitation to a grand party hosted by the enigmatic Count Suffle. The event takes place on a luxurious cruise ship, where guests are treated to an extravagant feast and entertainment. However, the festivities take a puzzling turn when the Count's prized treasure, the "Suffle Stone," is stolen. Oshiri Tantei is called upon to investigate the theft, which leads him to uncover a web of secrets and hidden motives among the ship's eccentric passengers.

As the investigation progresses, Oshiri Tantei employs his signature deductive methods, often involving humorous and unconventional techniques. The film introduces a colorful cast of characters, each with their own quirks and potential connections to the crime. These include the flamboyant Count Suffle, the suspiciously evasive crew members, and a variety of guests with peculiar behaviors. The story unfolds through a series of comedic interactions and clever twists, maintaining a playful tone suitable for its young audience.

The central mystery revolves around the true identity of the thief and the motives behind the theft of the Suffle Stone. Oshiri Tantei's investigation reveals that the stone holds a deeper significance, tied to the Count's past and the ship's history. The film balances its mystery elements with slapstick humor and light-hearted moments, ensuring accessibility for younger viewers while keeping the narrative engaging.

Throughout the film, Oshiri Tantei's unique personality and unorthodox methods drive the story forward. His interactions with Brown provide both comedic relief and moments of teamwork, highlighting their dynamic partnership. The resolution of the mystery ties together the various plot threads, culminating in a satisfying conclusion that reinforces themes of friendship, curiosity, and problem-solving.

"Eiga Oshiri Tantei: Sufūre-to no Himitsu" is a family-friendly anime that combines mystery, humor, and adventure, staying true to the charm of the original book series. Its straightforward narrative and endearing characters make it an entertaining watch for its intended audience.