Pokémon Season 1 Episode 37

The group come into a forest where they notice a large group of Pikachu that Ash's Pikachu tries to make friends with. Ash's Pikachu is welcomed among the other Pikachu as one of their own. Saddened by this sudden distance, Ash tries to leave Pikachu behind, thinking that it is going to be better off with its own kind.