Samuel "Sammy" Oak, a young Pokémon Trainer living forty years before the film's events, spent his childhood exploring forests and meticulously sketching Pokémon in his notebook, showcasing an early dedication to research. His life shifted dramatically upon encountering the Mythical Pokémon Celebi fleeing a forest poacher. Sammy intervened to shield Celebi, prompting Celebi to activate its time-travel powers and transport them both four decades into the future as escape. Disoriented in a Johto forest near Arborville, Sammy was discovered unconscious by Ash Ketchum, Misty, Brock, and Pikachu, who aided his recovery. Immediately voicing concern for Celebi's safety, Sammy revealed their bond formed during their escape from the past. He joined Ash's group in locating the injured Celebi and assisting its recuperation. Guided by wild Pokémon, the group traveled to the healing Lake of Life, where Sammy added future Pokémon sketches to his notebook, including a drawing of Pikachu and Celebi resting together. Sammy actively defended Celebi against the Iron Masked Marauder, a Team Rocket agent using corrupting Dark Balls. When Celebi was captured and corrupted, Sammy confronted the malevolent Celebi alongside Ash within the massive forest structure it created. Their efforts, combined with Suicune's intervention, shattered the Dark Ball's control. After Celebi's near-fatal collapse post-purification, Sammy observed multiple Celebi from across time reviving it. Following Celebi's restoration, Sammy returned to his original timeline with Celebi, sharing an emotional farewell with Ash and promising enduring friendship. Resuming his life, he preserved his sketchbook containing memories of the future adventure. Decades later, as Professor Oak, he retained vivid recollections. He comforted a disheartened Ash—who hadn't mentioned Sammy's name—after the incident, assuring Ash they would reunite. Oak later reflected privately while viewing the faded Pikachu-Celebi sketch in his old notebook. His experience with Celebi and witnessing Suicune also grounded his later anecdote to Ash about having seen Suicune once before. His childhood sketching directly influenced his future development of the Pokédex.