So can they be akumatized?
I think they can, but the miraculous' make them somehow undetectable, so only under the proper circumstances. How else would Hawkmoth not have found them by now? And how would the heroic team not have tracked him down? (Granted, they aren't even really looking but that's a rant for another time.)
My theory is this:
Adrien will realize that LB is just genuinely not interested and try to move on. (Though it will be hard.) Marinette will be on the verge of giving up on Adrien when he asks her out. (But they do have to become better friends in the upcoming season.)
They'll begin dating but still without any idea who the other's identity is. They'll just conveniently get up during a date at the same time when a need to transform happens.
Adrien: "Gotta go! I uh- forgot about something I need to take care of!"
Marinette: "Oh me too, uh- see ya!"
Adrien: "Want me to walk you back?"
Marinette: "Naw we're good, I've gotta go somewhere else first. Bye, see you tomorrow Charming!"
And that will go on for a while until one day it's Mari's birthday or an anniversary (Because we are still yet to see her birthday, it's got to be special).
Early on in the episode, it begins with a finished akuma attack. On the way out, Chat skips the fist bump and just leaves. He's just really excited for his plans to celebrate with Marinette and he's distracted by his excitement to surprise Marinette. Chat never skips the fist bump and for some reason it bothers Marinette this time and she doesn't know why. As she overthinks it, she has one of her famous dramatic freak outs (complete with background illustrations) she'll realize that she actually likes Chat.
Later, Adrien will call Marinette and ask her where she's at he has a surprise for her. (Probably a romantic dinner or something heartfelt and equally adorable, put together all by him self. So much adorableness the fangirling will be uncontrollable.) Marinette will let it go to voice mail a few times because she's down and confused. She's starting to realize she has feelings for Chat Noir but knows that isn't fair to Adrien. Adrien is the boy of her dreams after all, right? So why is this so difficult?
She'll eventually answer out of guilt. When Adrien explains he has a surprise for her she'll likely say that she's not in the mood for surprises and say she just wants to be alone. He'll get concerned and ask why, wanting to help her in anyway. (Because he's a good boyfriend and that's what they do.)
But Marinette can't tell him about her feelings for Chat Noir, that's absurd and might give something away. She'll make up a story or lie or get angry and defensive. She may not even remember it's their anniversary, she's that distracted.) Something about being clingy and why does it matter? They'll both hang up the phone angry and sad. Which makes them both likely to get akumatized.
Marinette is distraught for fighting Adrien, and for having shoved Chat away, he might be dating now! What is she gonna do! (Love square torturous feels!) Adrien will be disappointed in himself because he's lost both the loves in his life. But the real clinch is whoever takes off their miraculous.
I think the miraculous makes you somehow undetectable. Plagg doesn't care about any of this really, he just likes cheese and knows that the square is a very simple thing. But he has been trying to get them together. In Dark Cupid he grabs specifically Marinette's letter out of a stack the size of the Eiffel Tower. (Tikki and Plagg are so helping, but that is also another topic for later.)
So anyway, Plagg's comments are super unhelpful and annoying so he's likely to remove it to be alone. Tikki will be trying to give Mari comfort and advice, telling her what she did was a mistake and if she'll only call back it will all be better, etc. I do think Adrien is more likely to get akumatized. You can even go further into the story and have his Dad come in and ask what's wrong and he will say generally why and he'll tell him to just grow up and move on and leave the room. Hurt and angry, we might even see the butterfly go right downstairs from his lair. This might also be where another hero gets Qued in.
