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.
I can't comment without major spoilers. When you finish the golden age arc you'll see what I mean.
I've read all of Berserk, I'm just seeing how many "oofs" I could collect from people reading that.