Dual Hearts The plot begins with a treasure hunter named Rumble learning about a treasure, the Dream Stone on Sonno Island and setting out for it. At the same time, Tumble, who is a magical dream creature called a baku, is summoned by the Dream Queen to protect dream orbs. They both come to the same island and after a strange twist of fate become partners. Bakus can exist both within the dream world and the real world, and Rumble uses Tumble to travel into different peoples' dreams searching for the dream orbs. Most of the dreams become nightmares full of dangerous monsters.