Nanako Shichigusa (16) works as a maid in the hospital of Dr. Kyogi Ogami. Nanako is a classic ditzy slapstick protagonist who tends to accidentally break things and do everything wrong. Ogami treats her frequently in a cruel or heartless manner—threatening her, yelling at her and even subjecting her to physical abuse—yet at the climax of every episode he comes through to rescue her from whatever predicament she got herself into. Much of the series revolves around the relationship between Nanako and Ogami—his mean veneer, her faith in him, and how he alternates between the evil mad scientist archetype and the knight in shining armor archetype.

Scientist Ichiroubei Hiiragi discovers the existence of Six Gates, an otherdimensional world full of monsters and powerful hidden treasures known as Mon Mon Items. Ichiroubei embarks with his daughter, Rokuna, and her classmate, Mondo. However, they're foiled at every turn by Count Collection and his assistants, who want the Mon Mon Items in order to conquer both worlds. Becoming the heroes known as Mon Colle Knights, Mondo and Rokuna join forces with the monsters, striking back against Count Collection while searching for the Mon Mon Items in the name of friendship between their worlds.