OK it just popped in my head, among a bunch of other random shippy aus. It was originally just a headcanon, but it flowed into a drabble
But imagine Chat Noir and Marinette just hanging, or something random. And out of the blue, Chat gives her the direct number to his baton. Something only one other person has: Ladybug.
He tells her that anytime she needs a friend, just call him or text him. He may not answer imediatly but he will respond.
Marinette thinks it's silly and cute. When will she ever need to message him outside of costume.
But one day it does happen. Let's just say Chloe does something majorly cruel and she needs a friend. And Alya is busy with something with her family or something. So she calls him.
Chats in costume running patrol, so he picks up in 2 rings. Hearing the tears in her voice, he imediatly heads to her house. He stays there letting her bent about some bratty unnamed classmate (but he can guess since he witnessed the incedent) and just stays there. Consoling her and just being a good friend.
From that point it was different. Every so often, when they weren't doing a double patrol Marinette would get a text, usually at night from Chat wishing her good night, and she responding for him to stay safe. Something about his companionship touched her. Cuz in a ways he acted differently around Marinette than he did with Ladybug. He had a touch of insecurity just like she did about being Ladybug. She even began to wonder… did Chat Noir have many friends outside of his costume?
Her phone chimed. It was an evening wish from the cat himself, wishing her sweet dreams and a good day at school, accompanied by a cat emoji.
As she set her alarm she mused… what would he think if his friend Marinette was also Ladybug? She pushed that thought out of her head; not the first time that thought snuck in her head. And she rolled over taking one last look at the message before responding, wishing him the same.