As you were adventuring with your Pikachu, your Pikachu in question was playing on some rocks when it suddenly fell. As it landed on the ground, its eyes widened. Pikachu was engulfed in a bright white light, before standing back up…

But your Pikachu wasn’t a Pikachu anymore. It was a Raichu. As it stood up, a glimmer of light emerged from a smooth stone on the ground. It was a thunder stone

Raichu: "Rai…? Chu…?"