Dgc1808 on 17 March 2010
Pichu evolves into Pikachu after you level it up once when it loves you. Then Pikachu evolves into Raichu using a thunderstone. Pichu was introduced in generation 2 [Gold/Silver].
Plusle [the plus pichu you were talking about] and Minum [the minus] are just stand alone pokemon that don't evolve and are not evolutions of other pokemon. They were introduced in Generation 3.
4 ≈ One
