Chat Noir was partners with Ladybug. As such, he often noticed her little tics and her demeanor: she rubbed her wrists and flicked her fingers when she got anxious or happy. She stared into the distance on patrol a lot. She always ended up giggling when they kissed. She liked it when he rubbed his thumb over her knuckles when they held hands.
She also had a bit of a hot streak when it comes to akumas. She'd taunt them, trap them, and purify their akumas like it was nothing. She'd say a certain phrase whenever she got particularly invested or engaged in something: "Wanna bet?"
Akuma trying to trap them? "Wanna bet?"
Trying (and succeeding) to beat him in rooftop parkour, a game they made up to pass the time on patrol? "Wanna bet?"
Playing Cards Against Humanity on his birthday? "Wanna bet?"
So, imagine his surprise when he hears her trademark saying from Marinette. Sweet, innocuous Marinette. Let's set the scene:
Adrien rolled his pencil back and forth, tapping absentmindedly on his desk while the class chatted excitedly around them.
"Oh, please!" Chloe scoffed, examining her garishly painted nails and crossing her arms. "Ladybug would defeat Chat Noir any day! She's better than him in basically every way possible!"
Adrien winced at her harshness, although this kind of treatment from Ladybug fans wasn't uncommon. He was usually shoved to the side while microphones were jabbed in his lady's face.
Marinette's head whipped towards her. Adrien could practically hear her teeth grinding from the row behind her. The class went silent around her. They knew the drill. When Marinette's face darkened like that, she was about to go off.
She stood up, walking stiffly to Chloe's desk and slamming her hand down on the table. "What. Did. You. Say?"
Chloe flicked dust off of her shoulder, looking up at Marinette, who seethed with anger. "I said," She leaned closer. "That Chat Noir is useless."
"Wrong. Ignorant and wrong." Marinette lifted her hand from the desk, beginning to pace back and forth. "Chat Noir is just as, if not more, selfless and brave as Ladybug. He may not purify the akumas, but he's constantly protecting my- her back. She'd be dead right now if it weren't for his help."
Chloe sat straighter, not having expected a comeback. "Yeah, well, he's- uh- he got akumatized once-"
"He was just shot by Dark Cupid's arrow! He couldn't stop! And, if I remember correctly, he helped her in the end!" Marinette's hands were balled into fists at this point, and her face was red with anger. Adrien was shocked. When did Marinette get so devoted to him?
Chloe put her hands on her hips. "So? He's just her sidekick."
Marinette took a shuddering breath, silencing the whispers that had filled the classroom seconds before.
Chat lay on a small apartment ledge overlooking the dusk-shaded Parisian skyline. Yellow-orange light dappled his face. His eyes were closed, and he let his left leg and arm dangle off the ledge's precipice.
A thump sounded near his head, and he opened a cat-slitted eye lazily. "M'lady?"
Ladybug sat next to his head, threading her fingers through his hair. She didn't speak, just stared off into the orange-washed distance.
"Rough day?" Chat asked, reaching up to take one of her hands. She clasped heir fingers together. He squeezed her hand gently. They stayed silent in the lilac-scented air. A cool breeze slipped softly by them.
Chat hummed. "Want to talk about it?"
She sighed. "Sure." She took a deep breath, releasing it slowly as if to dissipate residual emotions. "So, there's this girl in my class. She started insulting you, and I sorta... kinda... lost it?" The way she phrased it sounded almost like a question. "I don't know. She said some crap about you being a useless sidekick and I went off on her."
Chat gasped quietly. No. No. It couldn't be. But the more his mind raced, the more dots he connected. The constant absences. The lack of sleep. Her vehement championing of him.
"Marinette?" The word tumbled out of his mouth before he could stop it, and he snapped it shut so hard he though a tooth broke.
"Hmm? Yeah? I mean-" She scrambled to think of an explanation. "Uh, who's Marinette?"
Chat sighed. "You can stop pretending, Mari."
Ladybug sighed. "What gave it away?"
"The anger. And the "wanna bet?" thing. And that speech- really impressive on the spot, by the way, m'lady." Chat sat up.