I thought the only way for Pichu to learn pain split was from the spiky-ear-pichu event in generation 4, and I'm pretty sure that event doesn't evolve as well. Showdown even says that Pikachu and Raichu can't learn pain split in generation 4 (if you type /dpplearn Pikachu/Raichu, pain split). Correct me if I'm wrong. Thanks :)