Sacha journeys to Alamos Town alongside Pierre and Aurore for a Pokémon Contest. Amidst the initial spatial disturbances from Dialga and Palkia's clash, he witnesses destruction in the garden and encounters Darkrai for the first time. When Baron Alberto attacks Darkrai, Sacha is struck by Dark Void. He endures a nightmare where he sees Palkia and plummets into an abyss with Pikachu, leading him to initially view Darkrai as a threat.

After recovering, Sacha joins other trainers battling Darkrai upon its reappearance in the town square. However, Tonio's revelation that Darkrai once saved Alice during their childhood, coupled with Sacha recognizing Palkia from his nightmare, shifts his understanding. He realizes Darkrai was attempting to warn everyone about Palkia's presence, transforming his perception of it from antagonist to protector.

As Dialga and Palkia's escalating battle threatens the town, Sacha takes decisive action. He and Aurore ascend the Space-Time Tower to activate the "Oración" melody, a song capable of calming the enraged Legendary Pokémon. Pikachu provides crucial assistance by charging the tower's mechanisms with electricity after initial power sources fail. Once the song pacifies Dialga and Palkia, Sacha pleads with Palkia to restore the damaged town.

In the aftermath, Sacha mourns Darkrai's apparent sacrifice during the conflict. His grief turns to relief when he witnesses Darkrai's survival atop the Space Tower, affirming its enduring role as Alamos Town's guardian.