A new villainous trainer group. They might see Ash as a threat to their plans of dominating the Pokémon world, so they kidnap him to stop him from competing in important battles or tournaments.
Ash could use his Pokémon. Pikachu, for example, could use its electric attacks to short - circuit any devices or barriers holding Ash captive. His other Pokémon like Charizard could also help by using their strength or special abilities to break free.
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.
There's also a possibility that it's a misanthropic Pokémon that just doesn't like humans interfering in the Pokémon world. It sees Ash as a symbol of human intrusion and decides to kidnap him with the help of the eevee to send a message to all human trainers.
Well, perhaps Pikachu would go on a heroic quest to rescue Ash. It might team up with other Pokémon like Charizard. They could follow the kidnappers' trail, facing various challenges along the way, like battling wild Pokémon or getting through difficult terrains.
One possible plot could be that Ash is kidnapped by a rival trainer group who want to steal his Pokémon. His friends then have to embark on a rescue mission, facing various challenges and battles along the way.
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.
I'm not aware of any non - inappropriate 'Ash gets a Pokemon pregnant' fanfiction. This concept is not in line with the family - friendly nature of the Pokemon franchise. Fanfictions usually revolve around themes like battles, training, and the bonds between trainers and Pokemon. A concept like this is quite abnormal and would not be easily found in the realm of proper fan - created works.
There may be some popular ones that have gained a following. For example, a fanfiction where Ash is kidnapped by an ancient Pokémon spirit that has been awakened and is angry at modern Pokémon training methods. This could attract readers because it combines the familiar Pokémon world with a new and strange concept. It might also include elements of Ash having to convince the spirit to let him go through his understanding of Pokémon.
In this fanfiction, it could be that Ash's marriage is a way to bring peace between different regions. He marries a princess or a powerful trainer from a rival region. Their union symbolizes the unity of Pokémon trainers everywhere. The story could then detail the political and social implications of their marriage, as well as the more personal aspects like their relationship building and how they learn to love and respect each other's Pokémon.