This is set sometime after the season 3 finale. Just how I think an identity reveal would go, after everything that's happened. Enjoy!
As Guardian, Marinette had thought it through and determined that it was probably best if she knew who Chat Noir really was. She was responsible for all kwamis and that included Plagg.
She had thought that perhaps only she should know Chat Noir's identity. A one-sided reveal. After all, she remembered very clearly what had happened in that alternate timeline. Somehow Chat Noir had found out who she was, and then wouldn't stop calling her by name. By her civilian name. In any case, telling him would be too risky.
That's what Marinette had originally decided. But when she'd brought it up to Chat Noir...the look on his face... She had never seen such a dejected look on his face before. Not even when she rejected him.
Marinette gave up caring about that other timeline. She would beat the importance of secrets into his head if she had to, but she would never let him feel like she didn't trust him. He was her partner, above all else.
She felt much better about revealing her identity now that he had a girlfriend. Marinette still remembered when he had first told her, nearly half a year ago. At the time, Marinette had thought Chat Noir was just trying to make her jealous again. She wasn't going to fall for the same trick twice.
He hadn't been lying. He'd stopped nearly completely with the nicknames. There was much less flirting and far more banter during fights. And most of all, he'd stopped asking her out. Chat Noir had gone from her best friend to someone she could count on, no matter the situation.
It had hurt a little, that just when she gave up her crush on Adrien, Chat Noir had given up his crush on her. Not that she had any right to feel hurt. She had rejected him numerous times. Once she was sure he actually had a girlfriend, she truly had been quite happy for Chat Noir.
It had helped that her own romance had been blossoming with Luka. He was calm, caring and just who she needed. It had started out with Marinette hanging out with Luka and Kitty Section whenever she got stressed. Whether her stress be from Lila or all her other responsibilities, the only way she could relax was listening to Luka play his guitar.
Kagami and Adrien would come over often too. Marinette hadn't gotten much time to really stay away, because she was Kagami's best friend. And after assuring the other girl that despite her dating Adrien, their friendship wouldn't suffer? Marinette couldn't stay away. It had come to a point that when she saw them together, she'd smile. Just like she would for any other of her friends in a relationship.
Honestly, giving up on liking Adrien had come as a relief. For one thing, they had finally become closer friends. The other was, she could relax. There was no need for her to feel so high strung all the time. No surprise, it made her grades shoot up, now that she could actually pay attention in school. She had so many things to be stressed about, even one less thing made all the difference."
She'd never thought it possible, but she was happy. The sound of footsteps behind her, made her spin around.
"Milady," Chat Noir bowed. He was shivering in excitement. Marinette smiled, she was too.
"Let's find a more secluded place."
"So the sewers?"
She laughed and nodded. Made sense, they spent far too much time in the sewers. Where else could they detransform safely anyways?
Far too quickly they had arrived. Marinette took a deep breath to calm her nerves.
"We don't have to. I mean you don't have to," Chat Noir offered. That only made Marinette smile. "No, let's do this."
They stood in front of each other. Unconsciously both closed their eyes as they called to remove their transformations.
They stood there, untransformed and eyes closed before Plagg cleared his throat.
Tikki chimed in, "You said you two were ready."
"We are!" Marinette insisted.
"Count of three?" Chat Noir suggested.
"One."
"Two."
"Three," the last one they said together as their eyes flew open. Marinette felt her jaw hit the floor.
"Adrien?"
"Marinette?!" Adrien sound as flabbergasted as she felt.
"You're Chat Noir? This whole time?"
"You're Ladybug! This is insane. How did we not know?" He paused. "Wait then who was Multimouse? How was Multimouse? What was Multimouse?"
"Huh? Oh that. That was just Trixx. More importantly, you're Chat Noir? You actually played yourself in a movie?"
"Hey, I was forced to!"
"You were going to play yourself in Clara's video. Mask and all!"
"I couldn't let Chloe play me! Plus so were you!"
He smiled smugly, infuriating Marinette. "You had a crush on me."
"Excuse me?"
"You, Marinette you, had a crush on Chat Noir. Though, I don't get the logic of confessing to my superhero self, when I was confessing to Ladybug all the time."
"I did not. I just made that up to make sure you didn't guess that I was Ladybug. I panicked, but it was your fault."
"My fault?"
"Yeah, who's suspicious of someone standing on their own balcony?"
Chat Noir, no Adrien flushed and looked away.
For all the banter, Marinette could still feel her head spin. "Oh it makes sense now," she murmured. If Adrien knew her identity, of course Chat knew who she was too. They were the same person.
"What makes sense?"
She shot him a stern look. "Now that we've revealed ourselves doesn't mean we use civilian names when in costume. Got it? No civilian names, no matter what."
Chat Noir nodded hurriedly. Then he frowned. "Hey, I just realized but...we're good friends."
"You just realized? Wow, I feel kind of offended," Marinette shot back.
"You know what I mean. I just...you always said there was another boy. How did I not know? I mean I'd say it was Luka but you said there was another boy even before we met Luka."
"O-oh. Um, that isn't important."
"It is to me," Adrien shrugged. "I wanna know who I got rejected for. I mean obviously he's an idiot considering you aren't dating him. I mean, you're amazing. Who wouldn't want to date you?"
You, Marinette thought silently. Then again, she'd spent who knows how long rejecting him. A laugh bubbled in her throat. Not a joyous laugh, but one that made you curse everything that existed in the world.
"Marinette?"
"I had the biggest crush on that boy. And I think you were the only one to not know about it."
"Just me?" Adrien sounded a little hurt.
She nodded. "But that's only fair considering the boy I was crushing on was you."
"Me? You were rejecting me for me?" He slowly repeated his sentence as if saying it again would make it sound any less crazy.
"We're ridiculous," Marinette sighed as she sat down against the wall. After a few moments, Adrien joined her on the ground.
"This whole time. So stupid." Adrien agreed. Then he looked at her sideways. "Did you ever consider me? I mean Chat Noir?"
"When I got over you. But by then you'd started dating Kagami." She looked at him, a bitter smile on her lips. "Don't worry. I already know you never considered me."
"What? Of course I did! But you had been dating Luka."
Marinette felt herself grow angry. "You considered me when you're dating Kagami?"
"What? No! Before that."
Marinette frowned, now confused. "Adrien, I only started dating Luka two months ago."
The look on Adrien's face almost made her start crying. He looked absolutely stricken. "So I kept myself from asking you out for nothing?" His face crumpled. "And now you've moved on?"
Marinette's voice caught in her throat. "I, haven't you?"
He paused, at a loss for words. Of all things, Marinette hadn't expected this to happen when she suggested finally doing an identity reveal.
She looked towards their kwamis, the two who had known the truth for so long. They seemed unsure of the problem. Plagg proved it when he said, "What's the matter? Now that you both know, you can be together and be happy. Well happier."
"We can't though," Adrien whispered. "Not right now."
"Maybe not ever," Marinette put in. "Kagami is my friend. You can't break up with her and then expect to date me. Besides, I have Luka. Who is your friend too."
"I know," Adrien nodded. Marinette had thought she was over him, but it felt as if her heart were breaking all over again. What a situation they had found themselves in. She loved Luka, she did. But Adrien had been her first love. And she was his, she knew that seeing the unshed tears in his eyes.
"No matter what happens, we'll always be friends," Marinette whispered.
He got to his feet and pulled her up too. Then he hugged her. "Of course we are. Maybe someday, sometime even something more. But for now just friends."
Marinette nodded before they transformed back into Ladybug and Chat Noir, leaving the sewers. They'd decided to head back home, both needing some time to come to terms with everything that they had learned.
Privately, Marinette didn't think there was much hope for her and Adrien. Luka and Kagami, meant too much to her now. She didn't want to have hope. It would be unfair for her relationship with Luka.
If it were meant to happen with Adrien, she'd accept it. But she wouldn't make any moves for it to happen. She was happy just being friends. Besides she remembered what Chat Blanc had said.
Their love would destroy the world. No, it was much safer for everyone if they just remained friends. Marinette liked it better this way. In fact, she preferred it. Right before she landed in her room, to go lay in her bed, Marinette wondered just who she was trying so hard to convince.
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