Mey - Rin could be a main character. Since she is a kind - hearted person, she would probably be very excited to take care of baby Grell. She might make little outfits for him and sing lullabies. And then there's Bardroy. He could be the one who is constantly worried about feeding baby Grell the wrong thing, like his cooking which is usually a disaster. But in the end, he manages to find some suitable baby food.
The Undertaker could also be a main character. He might find the whole situation of Grell turning into a baby extremely amusing. He could be the one who has some knowledge about how to reverse the transformation but doesn't tell right away. Instead, he enjoys watching the chaos that ensues with everyone trying to take care of baby Grell, and he might even play some pranks on baby Grell while the others are not looking.
Well, one possible plot could be that some sort of magic spell backfires on Grell. Maybe an experiment by a not - so - skilled wizard was meant to do something else but instead turns Grell into a baby. Then, the other characters would have to take care of baby Grell. They might struggle with things like changing diapers and feeding, all while trying to figure out how to turn Grell back to normal.
Obviously, Sonic himself would be a main character, even in his baby form. His friends like Tails, Knuckles, and Amy would also be main characters. Tails could be the one trying to figure out how to turn Sonic back. Knuckles could be the protector, and Amy could be the caretaker.
Obviously, Voldemort as a baby would be one of the main characters. Harry Potter could also be a main character as he has a long - standing enmity with Voldemort. He might be involved in deciding the fate of the baby - voldemort. Dumbledore would surely play a major role. His wisdom would be needed to deal with this strange situation. And Hermione, with her vast knowledge of magic, could be involved in trying to find a way to either reverse the transformation or ensure that the baby Voldemort grows up to be good.
Obviously, Ash would be a main character even in his baby form. Pikachu is bound to be a key character as well, being Ash's closest Pokémon partner. His other Pokémon like Bulbasaur, Charmander, and Squirtle could also play important roles in protecting and taking care of baby Ash.
His friends like Wade and Bob could be main characters. They would be the ones who first notice the change and try to help him. They might have some really funny reactions and also help him come to terms with being a girl. Maybe there could also be a mysterious character who caused the transformation in the first place and they have to find this person to reverse it.
Sherlock Holmes could be an interesting choice. Imagine the brilliant detective trying to figure out Grell's reaper nature and Grell being both fascinated and annoyed by Holmes' deductions. Their interactions would be full of intellectual sparring and comical misunderstandings.
Obviously, Shadow himself would be a main character even in his baby form. Sonic would also be a key character as he is often the hero in these Sonic - related stories. He would likely be involved in trying to figure out how to turn Shadow back. Tails could be another main character as his intelligence would be useful in finding a solution to Shadow's transformation. He might study the cause of it and try to come up with a remedy.
Obi - Wan Kenobi could be a main character. He was Anakin's mentor and would likely feel responsible for the baby, given his relationship with Anakin. He could be the one trying to guide the baby in the ways of the Force.
Conceptually, it might work if one were to find common elements between the two. For example, if Grell has certain magical or supernatural aspects, those could be integrated with the magic system of Harry Potter. But it would be a stretch as they are from different fictional origins.
Grell is often very well - written. Fanfiction writers can explore his complex personality, his unrequited love, and his wild nature in great detail. His over - the - top behavior and his unique take on death make him a fascinating character to write about.