Based on tumblr post: post/142369755494/miraculous-rival-au
The city of Paris was known for many things. It's monuments, the romance, the food, but mostly for its two biggest heroes: Ladybug and Chat Noir. Whenever a citizen of Paris became overwhelmed with any type of negative emotion, they could be possessed with a creature called an akuma and become a super villain. Thus, Ladybug and Chat Noir would come to save the day and purify the akuma.
But here's the catch: Ladybug and Chat Noir aren't on the same team. Never in the history of Paris has there ever been a more fierce rivalry than that of Ladybug and Chat Noir. As soon as an akuma arises, it's a race to save the day, and be the hero. Both have the ability to purify akumas, and both have a strong passion to save the day. No one knows how the rivalry began, but most people simply assumed it always was and always will be. Besides, good luck and bad luck could never be a team.
Now, that's not to say Ladybug and Chat Noir are against each other. They make no efforts to injure the other in their attempts to be the hero. In fact, it's not unheard of for one to apologize to the other if they accidentally hurt the other. No one likes apologizing to their rival, but they aren't cruel.
The rivalry of the fans was almost as fierce as the heroes themselves. The fans of Ladybug, called Littlebugs, were against the fans of Chat Noir, called Kitties. Alya was a staple of the Littlebugs, who ran the Ladyblog, which stared Ladybug with every post. There wasn't a blog as strong for Chat Noir, but Nino made a small blog for him just to jokingly spite Alya.
And of course, the real Ladybug and Chat Noir were strong in their team pride. Marinette, who was secretly Ladybug, gladly supported Alya's blog and agreed that Ladybug was, in fact, the best. Meanwhile, Adrien firmly believed that Chat Noir was way cooler and better for Paris. But of course, no one ever knew their identities, and to the rest of the world they just looked like normal fans.
The real fun starts when they start to become friends…