But what if Chloe and Marinette's relationship was more of a mutual rivalry that everyone in the class (excluding Alya) knows about since she's new? Adrien has some idea since Chloe talks about the rivalry a lot.
They banter, they argue, Chloe schemes, Marinette foils it, etc. There are a few times Chloe goes too far, but when she realizes that, she tries not to replicate it. Because Chloe isn’t as bad as in canon, Marinette is more confident.
Most of canon stays the same, but Chloe causes fewer problems and her redemption arc isn’t as, I don’t know the word, severe. She still has to unlearn some stuff and apologize when she goes too far, but she is generally nicer in this AU.
Alya doesn’t get what Marinette and Chloe's weird dynamic is, but it can be really entertaining, and she gets used to it pretty quickly.
The only reason I thought of this is because of two scenes that, when I thought of them, made me laugh a lot.
Scene 1: A couple of days after "Chameleon"
Chloe: "MARINETTE DUPAIN-CHENG!!"
Marinette: "Chloe? Wha—"
Chloe: "Don't you 'Chloe' me, you two-timer!"
Chloe: "I saw you trying to foil her schemes a few days ago."
Alya: "Lila wasn't sch—"
Nino: (eating popcorn) "Shhhhhh, things are just getting good."
Marinette: "Yes, but that's completely different!"
Chloe: "Really? That's your excuse? Different my ass! Are my schemes not dastardly enough for you, huh? You just had to get yourself a new rival."
Marinette: "What? No. I love stopping your plans!"
Chloe: "Well, your actions beg to differ. Do you know how many hours I spend trying to come up with my schemes so that you could foil them? After everything we've been through, I thought we had something special. I guess I was wrong."
Adrien, Sabrina & Alya: (cheering) "You tell her, girl!"
Marinette: "Alya?! You're supposed to be on my side!"
Alya: "I mean, you were accusing Lila of a lot of things, sooo...
"Chloe: "So, Dupain-Cheng, what do you have to say for yourself?"
Marinette: "Look, it's nothing really; her lies weren't even that good."
Lila: (offended) "HEY!!!"
Chloe: "If it's so unimportant to you, then you won't mind if I get a new rival."
Marinette: "WHAT?? WHO???"
Marinette: "KAGAMI?!?!?!"
And also this one based on an incorrect quote (includes Marigami):
Chloe: "I've seen that you've been spending a lot of time with Kagami lately."
Marinette: "No, Chloe, it's not what it looks like. I swear!"
Chloe: "Oh really? So, no reason for me to be jealous?"
Marinette: "No! You're the only one for me!"Chloe: "Is that so?"
Marinette: "I promise, Kagami and I are just dating, okay? They're my partner."
Chloe: "So there are no rival (best frenemy) feelings involved?"
Marinette: "Maybe for a bit, but you are still my one and only rival. They're just the love of my life."
Chloe: "But I'm still your arch-nemesis, right?"
Marinette: "Of course, Chloe."