Brock journeys as a central companion alongside Ash Ketchum and Misty to Arborville, prompted by witnessing the legendary Suicune near a riverbank. During this adventure, he joins the group's exploration of the forest after learning of Celebi, the mythical "Voice of the Forest," from local residents like the elderly Towa and her granddaughter Diana. His established background identifies him as a former Pewter City Gym Leader who relinquished the position to pursue becoming a Pokémon Breeder. By this time, he functions as the group's mature and knowledgeable figure, offering guidance and practical support. He carries essential supplies, prepares food for both humans and Pokémon, and consistently demonstrates a caring nature towards injured Pokémon, aligning with his broader aspiration to become a Pokémon Doctor. Within the film, Brock assists Ash, Misty, and Sammy—a boy displaced from the past—in locating the injured Celebi. He contributes to transporting Celebi to the healing waters of the Lake of Life, guided through the forest by wild Pokémon. His role remains supportive during confrontations against the villainous Iron Masked Marauder, who seeks to enslave Celebi using corrupted Dark Balls, emphasizing Brock's characteristic preparedness and focus on group cohesion. His well-documented tendency to flirt surfaces briefly with Diana, though Misty curtailed this behavior, reflecting a recurring series dynamic. Brock does not engage prominently in battles, instead emphasizing observational skills and logistical support. Following Celebi's restoration and Sammy's return to his own time, Brock departs Arborville with Ash and Misty.