>>57586692Cheren's arc is actually quite subtle especially when compared to Bianca's who everyone remembers because hers was quite in your face about it, well it also helped that during the confrontation with her father this song started playing
https://youtu.be/jzfQhV3G_MU?feature=shared.
The thing about Cheren is that he felt like the inverse of the jerk rivals where he starts off friendly enough, albeit thinking he's a know it all, there's a few moments especially at the beginning of the game with the professor. He also malds at Alder and doesn't understand why Alder is wasting his time wandering around the region. As he loses more to you he slowly starts to seethe more and more throughout although it's quite subtle. Alder and Marshal both help snap him out of it and if it weren't for them, his friendship with you and Bianca AND his Pokemon he would've gone full malding schizo jerk.
It's quite subtle it doesn't surprise me most people missed this.