One idea could be that a powerful magic spell backfires on Ash. His friends then have to take care of baby Ash while trying to find a way to reverse the spell. They might face challenges like getting baby Ash to eat Pokémon food or stop him from toddling towards dangerous Pokémon.
One possible plot could be that Ash wakes up one day as a girl and has to deal with all the changes in his daily Pokémon adventures. For example, he might have to adapt to new clothing styles and different social interactions. His Pokémon might also react in various ways to his new form.
Perhaps it's a prank gone wrong. A group of Gryffindors, thinking they could teach Draco a lesson, cast a spell on him that they thought would just embarrass him. But instead, it turns him into a baby. Now, Hermione, being the brilliant witch she is, feels responsible for finding a cure. She starts researching in the library, while Ron is left to keep an eye on baby Draco. Ron has no idea how to take care of a baby, and there are lots of comical moments as he tries to feed Draco and keep him from crying.
Maybe it starts with a strange magical experiment gone wrong in Hogwarts. Harry is curious and gets too close, and suddenly he's a baby. The story could then focus on how the teachers, especially Dumbledore, deal with this situation. They might try to figure out if this is a new form of dark magic they haven't seen before. And Harry, as a baby, would have no memory of who he is, so it could also be about his friends trying to make him remember bits of his past life.
In addition to the usual suspects, there could be some new characters introduced. For example, an old Pokémon trainer who has seen similar things before and can offer some advice on how to deal with baby Ash. Or a mysterious Pokémon that has the power to either help or hinder the process of getting Ash back to normal.
One possible plot could be that Ash is turned into a Pikachu by a strange spell cast by a mischievous Pokémon. As a Pikachu, he has to figure out how to communicate with his friends. His Pokémon pals at first don't recognize him, but Pikachu - Ash starts using his old battle strategies in a new way. For example, he tries to direct Pikachu's electric attacks in the same patterns he used to direct his other Pokémon's moves in battles. Eventually, his friends realize it's him and they set out to find a way to reverse the spell.
Well, one possible plot could be that his friends have to take care of him. Naruto might be really confused at first but then becomes super protective. Sakura could use her medical skills to make sure baby Sasuke is healthy. And they all have to figure out how to turn him back to normal while also dealing with the chaos that a baby brings.
Well, perhaps an enemy uses a magic spell to turn Zoro into a baby as a way to weaken the Straw Hat Pirates. At first, the crew is in chaos trying to deal with a baby Zoro. But as time passes, they see that baby Zoro has a pure sense of determination. He still tries to train, albeit in a very clumsy and cute way. And in the end, they go on an adventure to find the antidote to turn him back, with lots of comical and touching moments along the way.
Well, one possibility could be that a magical spell goes wrong in the world of the fanfiction. Maybe a young wizard was trying to do a simple transformation spell near Nico and it backfired, turning Nico into a baby. Then, his friends have to figure out how to reverse the spell. They might start by looking for ancient books in a hidden library that could hold the key to the solution.
Well, one possible plot could be that the other characters in the Solangelo universe are super confused at first. Percy might be all like 'Whoa, a baby Nico?'. They'd have to figure out how to take care of him. Maybe Will is the most determined to find a way to turn him back and in the process, there are some really cute and funny moments like baby Nico trying to grab Will's stethoscope and put it in his mouth.
Well, he might start to see the world from a Pikachu's perspective. For example, he would experience the small size and how everything looks so huge. He could also find it difficult to communicate with his human friends in the normal way since he is now a Pikachu. Maybe he would have to rely on Pikachu's ways of expressing emotions like using electrical signals.