When Lily died as a child, Mystique took her identity. What she didn't know was the fact that Lily was meant for something more. Mystique saw a child getting killed by someone else and decides to rescue the child. She was too late and buries the girl and then takes on the child's form and becomes Lily Evans. Mystique gets trained as a witch and marries James Potter. (Flarefury)

Pikachu had been transformed into a human girl from a type of powder that changes things into what ever the caster or curser wishes the victim to become. (Vidalark)