One possibility is that Marinette's family situation in Paris somehow leads to Batman adopting her. Maybe there was a threat from Hawkmoth that was too big for her to handle alone, and Batman steps in. He would then have to deal with her dual identity as Ladybug. He might try to keep her Ladybug activities a secret from the rest of Gotham, while also helping her to become a better superhero. It could be a story of growth, for both Marinette and Batman, as they learn from each other.
The story could explore how Marinette adapts to Gotham. With her skills as Ladybug, she could have some unique abilities to offer in Batman's city. Batman would probably be very strict in his parenting style, but also protective. He could teach her advanced combat and detective skills. And Marinette could introduce Batman to the more magical side of things, as she has experience with the Miraculous. It would be an interesting blend of two different universes.
Chapter 402, "The Survival Game Officially Begins!", is the clearest early answer because it turns Shen Lan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with What kind of face was it?
Chapter 153, "Word Spreads, Director Sun Takes the Lead in Shipping the CP!", is the clearest early answer because it turns Aunt Ying's situation into a concrete plot event. The chapter turns that into something concrete by moving from Wisps of smoke gradually rose from the small kitchen.
Chapter 470, "Why Talk About Pigs When Looking at Him?", is the clearest early answer because it turns Miss Bai Lu's situation into a concrete plot event. The chapter turns that into something concrete by moving from Wrapped in a bit of warmth, Jiang Yan slowly came to.
Chapter 148, "None are Normal", is the clearest early answer because it turns Director Zhang Cheng's situation into a concrete plot event. Early on, Exiting the cottage, Director Sun picked up the phone.. By the end, Just as Jiang Li put down her chopsticks, she received the call from....
Chapter 246, "Betting He Can't Last Even One Second", is the clearest early answer because it turns Hua Country's situation into a concrete plot event. The chapter turns that into something concrete by moving from At that moment, not only Su Yinwan but also Shang Shaojing's...
Chapter 449, "Do You Two Have to Be So Abnormal?!", is the clearest early answer because it turns Have's situation into a concrete plot event. Early on, Ahhh, the young master's good looks have finally returned!" "Wuwuwu,....
Chapter 177, "You Annoy Me Just By Being Here", is the clearest early answer because it turns Princess Disease's situation into a concrete plot event. The chapter turns that into something concrete by moving from I'm actually the last?!" After the scores were announced, Wen...
Chapter 356, "I announce, Lili is the best of the night!", is the clearest early answer because it turns Mr's situation into a concrete plot event.
Chapter 255, "Daton Festival", is the clearest early answer because it turns Uncle Zhao's situation into a concrete plot event. The chapter turns that into something concrete by moving from Sounds pretty interesting." "I know this one!
Chapter 122, "Qi Tianyu Scores Twice", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Damn, are we supposed to find the points card in the mud?!" He had...