A third-person action RPG, Dual Hearts tells the tale of Rumble and Tumble, an unlikely pairing of a young adventurer and a mythical creature known as a baku. While on a quest to retrieve the legendary Dream Stone, Rumble encounters Tumble, who is in fact on a quest of his very own. As ordered by the Queen of the Dreamworld, Tumble must safeguard nine ancient keys, whose combined powers ensure that nightmares remain sealed within the Temple of Dreams. The hapless creature loses the keys and the only way to recover them is to invade the dreams of people in the real world. Thus, the duo must seek out those whom they suspect have inadvertently become hosts to each key. While wondering around Sonno Island, players are free to speak to its many denizens or acquire items that will prove useful on their journey. As players wander about the island, time will slowly pass, changing from day to night and back again.