Atop the Raizen Mountains at [[Mount Tensei]], Ash's [[Rainbow Wing]] became corrupted when Cross appeared and placed it on Rainbow Rock with his evil heart. Marshadow in turn became corrupted by the Rainbow Wing and managed to possess a group of nearby Pokémon. Ash used Pikachu to battle against Marshadow, but the Gloomdweller Pokémon proved to be too powerful and it eventually won, but not without exhausting itself in the process. Ash grabbed the injured Pikachu to keep out of harm from Marshadow's army, only for the two to run into a dead end.
When Ash attempted to get Pikachu to return to his
[[Poké Ball ]] for safety, it refused. Pikachu, appearing to speak, revealed to Ash that it wished to stay by his side forever. Mirroring the start of their journey, Ash tried to protect Pikachu by standing in the way of the attacks. He eventually managed to recall Pikachu into his Poké Ball. Taking the full blast, Ash's body started to disappear, with only his consciousness surviving in a spirit world. Pikachu took hold of [[Ash's hat]] and started to cry, with the corrupted Rainbow Wing withering away, freeing Marshadow and the other Pokémon of its control.
Ash could hear Pikachu's cries in the spirit world and ran towards his voice. This caused his body to regenerate in the real world. Noticing this, Pikachu ran towards Ash and reunited with him, fully reviving him. After placing a new Rainbow Wing atop Rainbow Rock with his pure heart, Ho-Oh finally appeared. Ash and Pikachu had a fierce battle with Ho-Oh until the sun set. Some time after, Ash and Pikachu said their goodbyes to Verity and Sorrel, who continued on their own journeys. Pikachu continued to travel with Ash, aiding him in his dream to become a [[Pokémon Master]].