"Tottoko Hamutaro: Ham Ham Paradi-chu! Hamutarō to Fushigi no Oni no Ehonto" is a direct-to-video anime special that expands on the adventures of Hamtaro and his friends, a group of small hamsters who live in a world parallel to humans. The story begins when Hamtaro and his owner, Laura, visit a mysterious old house that is rumored to be haunted. Upon entering, Hamtaro and his hamster friends—collectively known as the Ham-Hams—encounter a strange, ghostly figure. This figure turns out to be a friendly but misunderstood oni (demon) named Oni-chan, who has been living in the house and is searching for a magical item called the Ehonto.

The Ehonto is a legendary treasure that holds the power to grant wishes, and Oni-chan believes it is hidden somewhere in the house. The Ham-Hams, intrigued by the mystery and eager to help, decide to assist Oni-chan in finding the Ehonto. Their search leads them through various rooms and hidden passages within the house, each filled with puzzles, traps, and challenges that test their teamwork and problem-solving skills. Along the way, they encounter other quirky characters, including a mischievous cat and a group of rival hamsters, who add to the adventure and comedic moments.

As the Ham-Hams delve deeper into the house, they uncover clues about the Ehonto's location and the history of the house itself. The narrative explores themes of friendship, cooperation, and overcoming misunderstandings, as the Ham-Hams learn more about Oni-chan's past and why he is so determined to find the Ehonto. The story culminates in a heartwarming resolution where the Ham-Hams and Oni-chan work together to solve the final puzzle, leading to the discovery of the Ehonto and the realization of Oni-chan's true wish.

The special retains the charm and lighthearted tone of the original "Tottoko Hamutaro" series, with its focus on the endearing dynamics between the Ham-Hams and their ability to turn any situation into an adventure. The narrative is driven by the hamsters' curiosity and their willingness to help others, making it an engaging and family-friendly story.