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.
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.
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 common theme is the idea of family. The dragon and the human child form a unique family unit, often defying the norms of both their species. Another theme is acceptance. The dragon has to accept the human child as part of its life, and the child has to accept living with a dragon, which is a very different kind of existence.
One interesting story could be about a powerful wizard who adopts a human child with special powers. The wizard teaches the child magic and they go on adventures together. Another might be a story where an alien adopts a human child and tries to understand human culture while raising the child in a very different environment.
The storyline could involve Rarity introducing the human child to the world of Equestria. She might teach the child about fashion and elegance, as that's her forte. The child could also learn valuable lessons from Rarity's friends, like loyalty from Rainbow Dash or kindness from Fluttershy.
Rarity would use her natural grace and poise to handle parenting. She'd start by dressing the child in the most stylish outfits, of course. And she'd likely be very strict about manners, as she values propriety.
First, create interesting characters. The adopter should have unique traits and the child should be relatable. For example, if the adopter is a dragon, give it a distinct personality. Then, develop a strong plot. Maybe the child has a special mission and the adopter helps them. Also, show the growth of the relationship between the two.
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.