https://tvtropes.org/pmwiki/pmwiki.php/Main/TheRival

7114519
Not a big fan of the trope due to how used it is in anime
In fact a big reason I was pleasantly surprised by black clover is that yuno was actually perfectly nice and a friend to asta despite them being rivals

Honestly, I'd say Cinder

7114522

7114528
But they never really hated each other

7114541
True but in Ruby's case I would want her to have a rival that made her angry so she can show an emotion other than happy

7114562
i think weiss could easily fit the role enough especially without being a full on rival

7114568
But would Ruby be the type to hold a grudge? I mean she's not exactly Ash Ketchum or Naruto