I have a theory.
We are yet to see the final few episodes of ash’s journey.
In those last few episodes, it will do a quick and cool fast forward thing where we see teen, and then adult, Ash. He will get with one of the Pokegirls he traveled with, probably Serena, or maybe someone new, and then have a child, that child being one of the main protagonists, more likely the girl as she shared some physical appearance traits with ash, mainly the color of the skin, hair, and design of the pin in her hair matching the one on ash’s hat.
TL;DR, Ash will be the father figure; the LITERAL FATHER of the main character.