It could be an Eevee. Eevee is a very common yet special Pokemon. It has the potential to evolve into many different forms, so it would be an interesting addition to Fem Ash's team.
Maybe it's a Pichu. Since Pichu is a baby Pokemon, it would be really cute if it hatched from the egg. Fem Ash could then raise it and watch it grow into a Pikachu or even a Raichu later on. Pichu is also very energetic and could bring a lot of fun to the story.
Well, she might take the egg to a Pokemon Center first. The Nurse Joy there could give her some advice on how to take care of it. Maybe she'll start to feel a special connection with the egg right away.
In this fanfiction, Ash could face a lot of challenges while taking care of the Pokémon egg. There might be other trainers or Pokémon who try to steal the egg. He would have to protect it at all costs. Also, he could meet some new friends who help him with the egg. They might give him advice on how to keep the egg warm and safe. And when the Pokémon finally hatches, it could form a really strong bond with Ash right from the start.
Well, in this kind of fanfiction, Ash might take really good care of the egg. He could keep it warm and protected all the time. Maybe he'd build a special nest for it. And when it hatches, it could be a super powerful legendary Pokémon that immediately bonds with Ash and helps him in his Pokémon journey.
Team Rocket would be the most obvious ones. They're always after rare and powerful Pokémon or Pokémon - related items, so the legendary egg would be a huge target for them.
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.
He might meet an old Pokémon expert who gives him tips on hatching the egg.
Well, Naruto might first be really confused about the strange Pokemon egg. He could try to figure out what it is and where it came from. Maybe he'd think it's some kind of new ninja tool at first.
In this fanfiction, Ash might take really good care of the Pokemon egg. He would probably keep it warm and safe, waiting eagerly for it to hatch. Maybe he'd even talk to the egg, like he does with his other Pokemon friends.
Well, in a story like this, Harry might first be really surprised to find the Pokemon egg. He'd probably try to figure out what it is. Maybe he takes it to his friends, like Hermione and Ron, and they all start researching about it together. They could be confused because Pokemon eggs are not from their world. Then, as the story progresses, the egg might hatch and out comes a cute little Pokemon. Harry would then have to learn how to take care of it.
He could meet some Pokemon trainers. They might come looking for the lost Pokemon egg and Naruto would have to decide whether to give it back or keep it.