Gupi and her friends enter an abandoned apartment in their building to deliver a cake. By passing through a closet in one of the rooms, they find themselves in a dark, unhappy, and otherworldly dimension. This place is home to the palace of the King Who Does Not Smile, whose sorrow has spread across the entire realm. Realizing that the inhabitants of this dimension have lost their joy because the King never smiles, Gupi begins trying various methods to restore happiness to the kingdom.