What if your starter Pokemon was actually a Ditto that got abandoned by it’s original owner because the owner kept telling it he wanted it to be a real Pokemon.
Everyday the owner would tell it “Why can’t you be more like a Bulbasaur? How about a Charmander? Why couldn’t you have been born a Squirtle?!” The poor Ditto spends months looking at these Pokemon and tried very hard to become one of these Pokemon. The master is displeased with it’s inability to stay a permanent shape for the rest of it’s life, so he releases Ditto.
As Ditto is left alone in the tall grass to fend on it’s own, it finally masters the permanent transform technique. Professor Oak one day stumbles upon Ditto assuming it is an actual Bulbasaur/Charmander/Squirtle and brings it to his lab. That faithful day you so happen to choose the one Pokemon that is your starter is actually a Ditto, and you start your voyage with it.
You love your starter to death you address it as a “him” or “her”” and it does everything to make you happy. But, sometimes when you look into your starter’s eyes you see a sadness that you try so hard to understand.
One day you wake up and your starter is walking down the road in the soaking rain and you call after him/her “Charmander/Squirtle/Bulbasaur please come back I love you!” Your Pokemon stares straight ahead and doesn’t look back at you. You pick up your starter and turn him/her around and see the face of a Ditto dripping colors of the starter’s face it impersonated. Tears well in it’s eyes and you realize Ditto is taking on the form of the starter you chose, because it fears you’ll leave it if it’s not something other than itself.
You realize your starter have much more in common than you ever thought. You squeeze the Ditto gently and tell it “Sometimes we’re afraid to be who we are but, when you are who you are I’ve never felt afraid.”