Misty is a very likely candidate. She has been with Ash from the early days of his journey. They have a deep bond and have shared many adventures together. Their relationship has always had a bit of a romantic undertone, so in a fanfiction, it would make perfect sense for them to get married.
Pikachu is a very likely candidate. It's Ash's most iconic Pokemon and has a deep bond with him. Whenever Ash is in trouble, Pikachu often steps up to protect him.
Ash is that energetic trainer we all know from Pokemon, always eager to take on new challenges and befriend more Pokemon. Astrid in Pokemon fanfiction can be seen as a fresh addition to Ash's world. She may be designed to add new dynamics to the story. Maybe she has a different approach to Pokemon training compared to Ash, like focusing more on Pokemon's natural instincts rather than just battle strategies. And she and Ash could start off not getting along but then gradually become good friends as they share experiences in the Pokemon world.
For Ash, Pikachu is always a great choice as it's his most loyal and powerful partner. Alongside that, a strong flying type like Charizard could be useful. For Brock, his Onix would be a staple. And perhaps a water - type like Vaporeon could be good for him to balance his team. Since they are teaming up, having a psychic - type like Alakazam could also be beneficial as it can help in battles and also with communication in tricky situations.
Ash could also have Charizard. It's a powerful and well - loved Pokemon of his. It could provide a lot of firepower in battles. For Gray, a Glaceon would be great. Glaceon's ice - type moves could complement Gray's more strategic style. It could freeze opponents and give Gray time to plan his next move.
Maybe it's a legendary Pokemon in disguise. In some fanfictions, legendary Pokemon often play important roles. It could give Ash the egg as a test or because it senses that Ash has a pure heart. Another possibility is that it could be a young trainer who can't take care of the egg anymore and trusts Ash to do a good job.
I think Lucario would be an interesting addition. It's a very intelligent and powerful Pokemon. It could sense danger and help Ash make better decisions. Also, Squirtle is a fan favorite. Its cute appearance and water - type abilities can add a lot of fun to the story, especially in water - related adventures.
Ash is of course a very common character as he is the central figure. Pikachu is also often included as it is Ash's most well - known Pokémon. Other characters like Misty and Brock might also make appearances as they are Ash's friends and travel companions in the original Pokémon series.