Serena could also be the one. She has a huge crush on Ash and has shown her love for him in many ways throughout the series. She is a kind and talented trainer, and her relationship with Ash has developed over time. It would be a sweet story if they ended up getting married in a fanfiction.
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.
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.
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 a possibility that she marries a Pokemon ranger. A ranger who has saved Jessie from a dangerous Pokemon situation. He shows her a different side of the Pokemon world, the side of protecting and co - existing with Pokemon. And when they get married, all the Pokemon in the ranger's protected area come to celebrate and offer their gifts, like rare berries or shiny stones.
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.
The plot could involve a threat to Alola. Ash and Lillie, now in love and getting married, have to put their wedding plans on hold to save the region. Along the way, they discover that their love gives them extra strength. They defeat the threat together and then have a grand wedding celebration, which is attended by Pokemon trainers from all over the world.
One possible plot could be that Ash and Ursula meet during one of Ash's travels. They start off as rivals but gradually develop feelings for each other. After many adventures together, they decide to get married. Their wedding could be attended by all their Pokémon friends, and they might start a new life exploring new regions as a married couple.
A plot could start with Latias being in some kind of danger, and Ash comes to her rescue. This leads to them spending more time together. As they get to know each other better, they realize their feelings are more than just friendship. After getting married, they might have to deal with people or Pokemon who don't approve of their relationship at first. But through their kindness and the strength of their love, they win them over and continue their happy life together.
Gary could also be the one to cause Ash's heartbreak. Maybe Gary outshines Ash in a big Pokemon battle and then mocks him for it. This could make Ash feel like a failure and break his heart. Gary has always been a bit of a rival to Ash, so this kind of situation is plausible in fanfiction.
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 the main character that we all know from the Pokémon anime. He is a determined and kind - hearted trainer. Ursula is the other key character here. She might be a less - known character or an original creation for this fanfiction. Their relationship forms the core of the story as they get married, so they are the main focus throughout the fanfiction.