In this fanfiction concept, Ash's adoption could be a very heartwarming story. Maybe he meets an orphaned child during his travels. Ash, with his kind heart, decides to take the child under his wing. It could be a chance for him to pass on his knowledge of Pokemon and values like friendship and perseverance.
If Ash adopts a child, the child could become friends with all of Ash's Pokemon pals. Pikachu could become like a big brother or protector to the child. Ash would have to balance his Pokemon training with taking care of the child. He might teach the child how to train Pokemon in a more gentle and understanding way, which could lead to new training techniques in the fanfiction.
One popular storyline is Ash having a child who inherits his passion for Pokemon. The child might start their own journey, facing challenges like Ash did, but also having unique experiences. For example, they could encounter new Pokemon species that were discovered after Ash's time. Another storyline could be the child trying to live up to Ash's legacy, which adds a lot of pressure and interesting character development.
Squirtle. Squirtle is cute and friendly. If it adopted a human child, it could show the child the underwater world of Pokemon. The Squirtle could teach the child how to swim, and they could explore underwater caves together. It would be a really fun and light - hearted story with Squirtle as the main Pokemon.
It could be an orphaned wizard child from a family that was killed by Death Eaters. This would give Snape an added sense of responsibility as he might feel guilty for being associated with the Death Eaters in the past.
Well, it depends on personal taste. Some people might like it because it offers a unique take on the Pokemon universe, with Ash having such an extraordinary origin. It can bring in new and exciting plotlines that deviate from the regular Pokemon storylines.
Team Rocket might be main characters as well. They could be constantly trying to capture Ash or his Pokemon because of his special status. Their bumbling attempts to take advantage of Ash's link to Arceus could add a lot of comical and action - filled moments to the fanfiction. And of course, Arceus itself could be a major character, guiding Ash in some way or interacting with him directly.
Maybe a Pikachu adopts a human child. The Pikachu is part of a group of Pokemon that live near a human village. The child was abandoned, and the Pikachu takes it in. They go on adventures together, with the Pikachu protecting the child from other wild Pokemon and teaching it how to communicate with different Pokemon species.
They expand the Pokemon universe. By introducing Ash's child, it allows fans to imagine what the future of the Pokemon world could be like. It also gives a chance to explore new relationships between characters and new storylines that keep the fandom fresh.
A major theme is the exploration of Ash's connection to the mythical Pokemon Mew. This can involve things like telepathy or special bonds with other Pokemon. Also, there's often a theme of destiny, as if Ash was meant to be something special because of his relation to Mew. And sometimes, there's a theme of secrecy, with Ash having to keep his true identity a secret from some characters.