Mon Colle Knights(2000)

Mon Colle Knights is an anime series following a scientist who discovers the Six Gates, an interdimensional realm teeming with monsters and magical treasures called Mon Mon Items. Joined by his daughter Rokuna and her classmate Mondo, he ventures into this strange world—only to face constant interference from the villainous Count Collection, who seeks the Mon Mon Items to dominate both dimensions. Transformed into heroes, Mondo and Rokuna team up with the monsters themselves to battle Count Collection's forces. Their quest becomes more than treasure hunting; it's about forging friendship between worlds and stopping a tyrant's conquest. Blending adventure with themes of cooperation and cross-dimensional harmony, the series follows these unlikely heroes as they navigate danger and discovery.