There could also be other characters from the TMNT 2012 universe that interact with the lone rat and cubs. Maybe some of the other turtles or their allies come across them and have to decide whether to help or not, which can add more complexity to the story.
The main character is obviously the lone rat. He is likely a key figure in the story, guiding and protecting the cubs.
The cubs are also main characters. They are the ones being cared for by the lone rat, and their growth and development can be a major part of the story. For example, one cub might be more adventurous while another is more cautious, and this can create interesting plotlines.
The Shredder could be a great main villain. He's always been a big threat to the Turtles and could pose an even greater danger to the cubs and the lone rat.
One idea could be exploring the relationship between the lone rat and the cubs in more depth. Maybe show how the lone rat teaches the cubs survival skills.
Another plot could be that the lone rat discovers a long - lost relative of the cubs. This relative could bring both hope and trouble. The relative might have knowledge that could help the cubs grow stronger, but also attract unwanted attention from the rat's old enemies.
Most likely, the main characters would be the Teenage Mutant Ninja Turtles themselves - Leonardo, Donatello, Michelangelo, and Raphael. They are the core of any TMNT story.
Well, of course, the Teenage Mutant Ninja Turtles are likely to be main characters. They are usually Leonardo, Donatello, Michelangelo, and Raphael. And then there's the OC (Original Character) who is in the jungle setting. The OC could be a human, another mutant, or some other kind of being.
Some fanfictions might introduce new characters as friends or allies of the little sister. For example, there could be a street - smart kid who helps the little sister understand the human world better since she's growing up in a rather unusual family. But the main focus always remains on the relationship between the turtles and their little sister.
His friends like Hermione and Ron could also be important characters. Hermione might use her intelligence to help Harry during the pregnancy and after the birth, while Ron could provide some comical relief with his typical reactions.
Splinter is also likely to be a main character. He is the turtles' master and mentor, and his wisdom often guides them in difficult situations. In this fanfiction, he might play a crucial role in helping the turtles face new challenges.
While Mikey and Donnie are the main focus, sometimes their older brothers Leo and Raph can also play important roles in the fanfiction. For example, they might be searching for the missing baby turtles, or they could be the ones who teach Mikey and Donnie important lessons when they finally reunite.
Obviously, the four main Turtles - Leonardo, Donatello, Raphael, and Michelangelo are going to be main characters. They are the core of any TMNT story. They'll probably be the ones interacting with the other versions of themselves in this 'Meet the Turtles' concept.