While playing in a forest, Pikachu, Dedenne, Froakie, Fennekin, Chespin, and Hawlucha discover a sparkling golden key attached to Dedenne's tail. A wild Klefki, the Keyring Pokémon, appears and snatches the key, but finds it stuck to Dedenne. After a brief tussle, Pikachu offers the key back to Klefki, and Klefki rewards them by using its keys to open a floating keyhole in the air, revealing a portal to a strange new dimension.

Klefki leads the group through a series of pocket dimensions, each tied to a different mystical Pokémon. The friends explore surreal landscapes, including a crystal cavern, a starry sky, and a forest of floating islands, encountering Mythical Pokémon such as Manaphy, Darkrai, Jirachi, and Victini along the way. Each encounter is peaceful and wondrous, with the Mythical Pokémon briefly interacting with the travelers before the journey continues.

The narrative arc is a lighthearted exploration of friendship and curiosity, as the group moves from one fantastical world to another, guided by Klefki and the keys it holds. No major conflict arises; the story is driven by the joy of discovery and the bond between the Pokémon as they navigate the ever-changing environments. The short concludes with the group returning to their own world, the mystery of the key resolved through the shared adventure.