Marinette's parents come to Gotham for a Wayne Gala. There Marinette becomes friends with Bruce.

But her parents are murdered on their way to hotel. She cries hard in that alley which was near a zoo and Quinzels found her.

So Marinette is let's say adopted by the quinzels or rather Harley as a sister and becomes Marinette Quinzel.

She becomes best friends with her new sister Harley.

They both love psychology. Marientte and Harley together learn psychology and made cute dresses for the animals. They both love the zoo etc etc.

Instead of Harley, Joker was assigned to Marinette.

She becomes MariDuChen (just take the front letters of her name).

In real she just wants to save Joker. She goes deep into the darkness thinking she can pull him out.

Bruce is devastated when his best friend becomes crazy. He was going to propose to her but instead he came to know that she's a villain now.

So his blood of course boiled whenever Joker touched her, hurted her, kissed her and bla bla bla.

Harley goes to save her sister but the joker ordered her to kill her own sister. She missed the heart because that's her best friend, her sister. But put Harley in a coma because of the injury.

So Batman struggling to fight with Joker and MariDuChen because his traitor heart squeezed whenever he saw Joker do things to Marinette's mental and physical state.

Joker always throws Marinette at Batman to run and it worked every time.

Maybe after knocking her out he once or twice hugged her, begging her to come back or maybe he just doesn't know that it's her.

Well and you know the "wrap me in plastic" song fic, that stuff.

If we want to include miraculous, it can be that she got it from her "uncle" Fu. So she saved the Paris with Harleen as her black cat. She becomes the temporary miraculous box.

But the small logical sane part of her stopped her from using the miraculous.