"Tottoko Hamutarō: Ham Ham Ham - Jya! Maboroshi no Princess" is a direct-to-video anime special that expands on the adventures of Hamtaro and his friends, a group of anthropomorphic hamsters. The story revolves around a mysterious and magical event that transports the hamsters into a fantastical world filled with adventure and intrigue.

The narrative begins when Hamtaro and his friends discover a peculiar golden seed in their garden. Upon planting it, the seed grows into a massive sunflower that emits a dazzling light, transporting the group to a magical kingdom. This kingdom is under the rule of a benevolent but troubled princess named Princess Laura, who bears a striking resemblance to Hamtaro's human owner, Laura Haruna. The kingdom is plagued by a dark force led by the sinister King Spat, who seeks to steal the kingdom's source of light and power, the Sunflower Crystal.

Princess Laura reveals that the Sunflower Crystal is the key to maintaining peace and prosperity in her realm, and its theft has caused the kingdom to fall into chaos. She enlists the help of Hamtaro and his friends to retrieve the crystal and restore balance. The hamsters, eager to help, embark on a journey through various magical landscapes, encountering both allies and adversaries along the way. They face challenges such as navigating treacherous forests, solving puzzles, and outsmarting King Spat's minions.

Throughout their quest, the hamsters demonstrate teamwork, courage, and resourcefulness. They meet new characters, including a wise old hamster sage who provides guidance and a group of rebel hamsters fighting against King Spat's tyranny. The story emphasizes themes of friendship, bravery, and the importance of standing up against injustice.

The climax occurs when Hamtaro and his friends confront King Spat in his dark fortress. Using their combined strengths and clever strategies, they manage to retrieve the Sunflower Crystal and defeat King Spat, restoring light and harmony to the kingdom. Princess Laura expresses her gratitude, and the hamsters are celebrated as heroes. The story concludes with the group returning to their world, their bond stronger than ever, and the magical sunflower serving as a reminder of their extraordinary adventure.