Satoshi journeys to Alamos Town alongside Takeshi and Hikari to compete in a Pokémon Contest. Alice, a local tour guide and music student, greets them upon arrival, guiding them through the town and its harmonious Pokémon garden. A disturbance erupts from a dimensional clash between Dialga and Palkia, prompting an encounter with Darkrai, a Pokémon infamous for nightmares. Satoshi experiences a nightmare vision triggered by Darkrai, depicting Palkia's assault and Pikachu vanishing into a void, fostering immediate distrust.

Later, Satoshi observes Darkrai actively shielding the town from Palkia and Dialga's escalating battle, which warps space-time and envelops Alamos in fog. Despite Baron Alberto's accusations against Darkrai, Satoshi reconsiders after Tonio reveals Darkrai once saved Alice from a childhood accident. This revelation transforms Satoshi's view, leading him to recognize Darkrai as a guardian.

As the conflict worsens, Satoshi aids in coordinating the town's evacuation and joins the mission to play the calming "Oración" melody on the Space-Time Tower's organ. During the ascent, he witnesses Darkrai intercepting Dialga's Roar of Time attack to protect the group, an act that gravely injures Darkrai. Satoshi and Hikari press onward on foot, reaching the organ and successfully performing the melody, halting the legendary battle.

Satoshi's actions display his trademark determination and readiness to revise initial judgments based on evidence. His role focuses on mediating the conflict by discerning Darkrai's true protective nature and enabling the resolution through the Oración melody.