Diamond and Pearl, gender differences were introduced; a female Pikachu now has an indent at the end of its tail, giving it a heart-shaped appearance. They attack primarily by projecting electricity from their bodies at their targets. Within the context of the franchise, a Pikachu can transform, or "evolve," into a Raichu when exposed to a "Thunder Stone." In later titles, an evolutionary predecessor was introduced named "Pichu", which evolves into a Pikachu after establishing a close friendship with its trainer.