So, I'd like to point out that I'm not a big Dr. Who fan, but this idea hit me, and so I might do a few more scenes of this AU.
Basically, Ladybug and Chat Noir are like the Time Lords, but I'm taking significant liberties, so the lore is going to be much different. It's mostly just playing around with the characters, and hopefully some epic scenes.
Alya had never had a day like this before. She was a reporter, and that meant seeing a lot of weird things, but the most she was expecting while out on a date with her boyfriend, Nino, was maybe seeing a few oddly-dressed tourists. She didn't expect to see an alien invasion by geometrical shapes pixelating people. She didn't expect to be rushing an old woman who was apparently a former WWII Freedom Fighter to the hospital amid the chaos, and she really didn't expect to run into a girl her age, looking a lot like the old woman, chasing off the aliens and reversing the "pixilation" of the victims, and now rummaging through the old woman's stuff while everyone else was still outside trying to figure out what was going on.
"Hold these," came the command as various jackets and hair ties were shoved into Nino's arms. Grabbing a purse, she opened it up and pulled out a card, an ID Alya got a glimpse of and swore that it looked different before. "'Marinette Dupain-Cheng'? Did you have to give me a pun for a name, Tikki?"
"Why are you rummaging through an old lady's stuff?" Alya demanded, pulling out her phone in case she needed to start recording theft.
"It's actually my stuff," the girl, Marinette apparently, answered. "Explanations later. Work now. I need this." Alya's phone was deftly snatched and Marinette dialed a long number before either Alya or Nino could protest. "Hello. You Idiot. Did I say you could go? Articles of Creation, Section 42. This is a fully-developed, Level 5, M-class planet. Did you really think no one was watching? Do you think simply returning everyone absolved you? Get back here. Now!"
The phone was tossed back to Alya, who was grabbed by the dark haired girl and pulled along with Nino. "Did you just call them back?" the DJ asked. "You save the world from aliens, and you call them back."
"Just the one," was the answer as they were pulled to the stairwell. "He does everything via automation. We're meeting him on the roof."
"With someone else's clothes?" Alya repeated.
"My clothes. They change as often as I do. Pretty sure Tikki has a bad sense of humor though. She knows I hate puns."
Confused and getting no answers, both Alya and Nino were reluctantly pulled to the roof, where Marinette grabbed the pile of jackets and ribbons Nino was carrying and walked purposely forward to the floating pyramid hovering above. "This is a good idea?" Nino asked again. "They were leaving."
"Leaving is good. Not coming back is better."
A pixel effect blurred between them, revealing a young man who looked like he stepped out of a Cyberpunk Convention. He tapped his odd glasses and a beam shot out, running over Marinette as she smirked. "Hello, Gamer."
"You are not of this world."
Alya and Nino looked at each other. Two aliens? What had they been caught up in?
"No, but I've put a lot of work into it," Marinette answered, looking at the ties in her hands before settling on the pink ones and tossing the rest to the winds.
"Is this world important?" Gamer asked.
"Important?" she scoffed. "What does that word mean? 'Important'? There are billions of people living on this planet. Is that not 'Important'? Here's a better question, Gamer. Is this world a threat to you?" The two extrahumans stared at each other for a while before she probed again. "You're monitoring the whole planet. Is this world a threat?"
Gamer's pyramid began projecting a hologram between them, showing the globe of Earth.
"No."
Having finally picked a jacket, red with black spots, she tossed the rest back towards Alya and Nino. "Are the peoples of this world guilty of any crime according to your laws?" she asked.
The hologram shifted, showing various images of what are, perhaps, the most disturbing moments of human history. Images of wars, death, riots, and mass executions passed in mere moments.
"No."
Now that was a surprise. All that, and humanity wasn't guilty of any crime?
"All right," Marinette said while straightening her pilfered (at this point, Alya wasn't sure) clothes. "One more question. Just one more. Is this world Protected?"
The images in the hologram changed, showing an army of massive golems, a shadowed figure with a glowing butterfly symbol releasing a malevolent swarm, black-armored knights marching in step, a flood of gremlin-like creatures, mummies, pigeons making abnormal shapes, a mermaid swimming through a flooded city, and many others while she continued to speak. "You're not the first to come here, are you? No. There have been so many more. The thing you need to ask is: 'What happened to them?'"
She stepped away while pulling her hair up and beginning to tie it, as a series of people began flashing in Gamer's hologram. A humanoid figure of light and energy. An Egyptian queen. A Chinese warrior. A OmuHimba. A female Spartan. An Amazonian. An Aztec prince. A cloaked assassin. A female Musketeer. A Vietnamese girl Alya didn't recognize. A female knight she did recognize as Jeanne d'Arc. A Mexican dancer. A WWII Resistance Fighter. Each one was different and yet each one was wearing something that was red with black spots, and in spite of their differences, they all looked incredible similar to...
Marinette deliberately stepped into the hologram, forcing Gamer to dispel it as she stood before him proudly. "Hello. I'm Ladybug."
Alya heard Nino gasp next to her as her jaw dropped, the realization coming to both of them at once. This was no mere girl who had rummaged through an old lady's stuff. She was the old lady, as well as every person they saw in Gamer's hologram. A single being reborn anew over and over again. Someone who had touched humanity in the past, inspiring myths and legends, yet somehow historians never connected them all together as being one single entity. She was beyond Gamer the way Gamer was beyond any mere human.
Marinette... Ladybug... was a God.
"Basically," said entity began, closing her eyes. With her back to Alya and Nino, the two wouldn't see. But Gamer did. Her eyes opened and were no longer blue, but blood ruby read with five pupils in a Ladybug motif.
"Run!"
To his credit, Gamer didn't flinch, but he got the warning loud and clear. Within seconds he had pixelated back into his pyramid of a ship and was flying away. Even without her other half, Ladybug was a force to be reckoned with, and she had a long memory. Given that she now looked young, almost too young, that meant that she had recently been regenerated.
And that meant someone was possibly doing something with the Black Cat, and Gamer did not want to be around when Creation and Destruction dealt with whomever was trying to control something that would never be controlled.