In a world where humans and monsters coexist, a young man named Mephiles must find a way to stop the return of his brother, Mephiles II. The story follows their complicated past and the events that led to the current state of the world.
The gameplay in Sonic Unleashed is an action-packed mix of exploration, platforming, and combat. Players control Sonic as he explores the city and faces various enemies, from ordinary humans to monsters like Werecats and Werebadgers. The game features a unique "Dark" and "Light" form that Sonic can transform into, allowing him to access new areas and fight more effectively.