Now, I had more than a few ideas for this one, but in the end I opted for a little talk between the Lila and the Chat Noir of that AU. One that tackles the fact the series is set in France, with their own rules for certain things…
WARNING: Also set in an AU where Lila showed up right at the first episode and things went a bit differently… Including Master Fu giving out three Miraculous on that day. Not in chronological order.
Day 7: MariHarem
"Red roses, chocolate from the best bakery in Paris… This is all quite expensive." Lila commented after looking over the list of things Chat Noir had asked her to purchase. "I'm not going to ask you where you're getting the money, but are you sure she's worth it?"
"Of course! She's Ladybug!" he replied, almost offended.
"Yes, I suppose she'd-wait, Ladybug?!" This was bad, really bad. Chat Noir was the only competition she had any reason to fear. Well, he and Adrien Agreste, but between Zoe the Fangirl, Chloe, and his apparent crush for Marinette that he was too oblivious and naive to notice, he wasn't a danger. "Since when?!"
"Since ever? I mean, why would I flirt with her so much? And I know she feels the same!"
"And now I've just learned your parents are very strict and homeschooled you for most of your life, possibly even now, and Ladybug and Vorpika were among your first friends if not the first."
Chat Noir flinched. He knew Lila was smart, likely as much as Ladybug and Vorpika, but he didn't expect her to suddenly guess that.
"How do I know, you wonder?" Lila asked, before answering herself. "Because otherwise you'd have learned the French dating rules, and not the Americans. Things such as no third date rule, no dating protocol period, men and women flirting all the time even as friends(1)…" Almost reflexively, Lila took a picture of Chat's face before continuing. "And if you think I'm trolling you, think about my class and explain why otherwise Chloe would allow anyone but Adrien to flirt with her, or why Kim and Alix spend half their time flirting even when the former has a girlfriend."
"Oh." Chat said, before remaining silent for a while. "I-I suppose I owe you, you saved me from an embarrassing situation…"
"Don't worry. With all the time you spend saving my class, I suppose we're friends-and friends help each other."
The fact Lila had her own reasons to keep Chat Noir from declaring himself to Ladybug went unsaid. Or completely unnoticed by Chat.
Author note
(1)This was something I wanted to point out for a while: French have a different dating system from the Americans that make up so much of the fandom. Hence why Chat Noir thought Ladybug was leading him on and Ladybug/Marinette didn't even know he had a crush on her until Chat told Mari: in France it's perfectly normal, just as a man and a woman going out together alone as friends, even when married. Luckily for me they're almost the same as the Italian ones, so I have no issue with them… And I can proclaim that Marinette's kiss in the second season finale was of romantic nature. Not that Adrien would know the difference, what with his hyperprotective parents and his only friend for years having been Chloe…