It depends on how you define 'real'. Some aspects might be based on real-life experiences, but it could also have fictional elements for entertainment purposes.
Mikey might be a character created to tell a story about Pop Rocks. He could be a fictional child used to illustrate the appeal or novelty of these candies. For example, he could be a curious and adventurous little boy who wasn't afraid to try new things, like Pop Rocks, which were quite different from other candies at the time.
April and Casey might also be part of this fanfiction. April could use her reporting skills to try and figure out what's going on with Mikey's mutation, and Casey would be ready to fight any new threats that come along because of Mikey's changed state. Also, Splinter, as their sensei, would be guiding them all through this difficult time, providing wisdom and training to help Mikey control his new powers if he has any.
I'm not entirely sure specifically as there could be many things. It might be a type of fictional works created by Nicky Pellegrino that are full of imagination and interesting stories.
Fanfics like'mikey x raph fanfic' are really interesting. They give fans the opportunity to expand on the existing relationship of the characters. In this case, it might explore how Mikey and Raph support each other in ways that the original source material doesn't fully show. It could be a story full of humor as Mikey cracks jokes and Raph reluctantly smiles, or it could be a more serious exploration of their bond during difficult times.
One common theme could be friendship development. Maybe they start as acquaintances and gradually become close friends, sharing secrets and having adventures together.
One great 'raph x mikey fanfiction' is 'The Bond Beyond Brothers' on FanFiction.net. It delves deep into their relationship, exploring how they support each other during tough times in the Turtle universe.