The rival.
Especially the douchebag Machiavellian type rivals that the main character ends up friends or teaming up with after the main character 'proves their worth' to them by being stronger. No character growth outside of now they work with the protagonist.
I really want this trope to be subverted one day, like the douchey rival shows up and everyone is just like "Wow what a dickhead" and just relentlessly bullies him until he goes away.
He follows the arc of Blue, in which he just grows up and gets a fucking job. Meanwhile Red is like a hermit I dunno.
"A volcano erupts, and just like that, a whole town disappears. We can go on winning and losing in Pokémon, but if nature so much as twitches, we can be overwhelmed in a second…" -Blue in Gold/Silver/Crystal
That's a hell of a character arc from "Smell ya later!" ~jaunty music~