Make up a personality for your characters based on their in game actions.

Based on what he does throughout the entire game, I can safely say that Elio is perpetually high or gives zero fucks about anything. In a matter of days, he beats every trial captain, kahuna, elite four member, saves the world, and not once ever changes that smile on his face. He doesn't so much as frown when Lillie leaves to Kanto, so it's safe to say that he's pretty much a sociopath.