Their relationship would become more mature. They would have to rely on each other more than ever. With a baby, they'd have to share responsibilities, which could lead to a deeper understanding and respect for each other.
The plot could involve Ash and Serena finding a baby Pokémon that is in a situation similar to being an orphan. Since they have such a strong bond, they decide to take it in and raise it as their own. They then have to learn how to take care of this special Pokémon baby, which includes finding the right food, a safe place to live, and teaching it important skills. Their friends from their Pokémon adventures might also get involved, some being supportive and others being a bit skeptical at first.
There are many ways fanfiction writers can take this concept. They could write about the baby having special powers or a unique connection to Pokemon. It could also be a story about the family traveling together, with Ash and Serena passing on their knowledge and values to their child. This type of fanfiction can be a great exploration of family dynamics within the Pokemon universe.
One possible storyline could be that Ash and Serena settle down in a peaceful region, perhaps near a forest. They start their family life and the baby could inherit Ash's love for Pokémon battles and Serena's grace. The baby might grow up surrounded by Pokémon, learning about different types and their behaviors from a very young age.
One idea could be that their baby has a special Pokemon - like a Pikachu that was born with a unique marking. It could start to show amazing abilities from a young age, and Ash and Serena have to figure out how to help their baby train it.
One aspect could be the naming of the baby. Since they live in the Pokemon world, the name might have some connection to a Pokemon or a special place they've visited. Also, the story could involve the baby's first encounter with a Pokemon, which could be a really cute and heartwarming moment.
Their friends would be overjoyed. Brock would probably offer his medical knowledge to make sure the baby is healthy. Misty might be a bit jealous at first but would soon warm up and offer to teach the baby how to swim. Clemont could create some amazing gadgets for the baby, like a Pokémon - themed mobile or a stroller that can move on different terrains easily.
Another idea for a fanfiction could be that Ash and Serena's baby is born with a special power. This power attracts different types of Pokemon to it. As the baby grows, Ash and Serena have to figure out how to control and use this power for good, all while protecting the baby from those who might want to misuse this power.
Their Pokémon would probably be very protective. Pikachu, being Ash's closest companion, would always be on guard around the baby. It might even try to play with the baby in its own cute way, like using its electric shocks to create little light shows to amuse the baby. Serena's Pokémon, like Fennekin which evolved into Delphox, could use its psychic powers to sense if the baby is in any danger or discomfort. All of their Pokémon would likely adapt their usual habitats and behaviors to be more baby - friendly, for example, making sure not to use any dangerous moves near the baby.
You should also consider the setting. Will it be in the familiar regions from the Pokemon world, or a new, made - up place? If you choose an existing region, like Kanto, you can add in elements from the original series, like having the baby interact with the local Pokemon in a unique way. Then, create a rough outline of the story, including the main events and how the characters will develop.