Well, when Ash travels back in time in fanfiction, his Pokémon team can change in several ways. He could end up with Pokémon that he had lost in his original timeline. Maybe a Pokémon that evolved and left his team in the present could be with him as its unevolved form in the past. Also, he might catch Pokémon that he previously only dreamed of. For instance, he could have caught a shiny Pokémon that he never had the chance to in his original journey. His team could also be stronger overall because he has the knowledge of how to train them better from his future experiences.
In Ash travels back in time fanfiction, his Pokémon team often changes significantly. Firstly, he may add Pokémon to his team that he never had before due to his knowledge of future Pokémon encounters. He could also prevent the release or loss of some of his Pokémon from his original journey. For example, if he knew in advance that he was going to release a certain Pokémon in the future, he could avoid that situation in the past. Moreover, he might be able to evolve his Pokémon earlier or in different ways because he has learned new training methods in his future adventures. His team composition could become more diverse, including Pokémon from different generations and regions, which gives him an edge in battles and adventures compared to his original timeline.
In some fanfictions, Ash might have a completely different starting Pokémon team. For example, if he goes back far enough, he could start with Pokémon that were rare in his original time. His Pikachu might not be his first Pokémon. Also, he could have Pokémon from different regions right from the start. He might have a Sinnoh Pokémon like Piplup instead of a Kanto Pokémon as his initial partner.
The unique character development. When a Pok mon is pregnant in a fanfic, it gives an opportunity to explore the Pok mon's personality in a new light. For example, how it copes with the physical and emotional changes. It can also show the relationship between the Pok mon and its trainer in a different way, like increased protectiveness from the trainer.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. These platforms have a wide variety of Pok mon fanfics, and you can use the search function to specifically look for ones related to the 'pregnant' theme. Just be sure to read the ratings and reviews to ensure the quality.
One popular plot could be Ash going back in time to the very beginning of his Pokémon journey. He might use his future knowledge to catch Pokémon more effectively, like getting a Pikachu right away without the initial reluctance. Another plot could be him traveling back to save a Pokémon from a past disaster that he couldn't prevent in his original timeline. For example, he could go back to stop the destruction of a Pokémon habitat that led to the endangerment of a certain species. A third popular plot might be Ash traveling back to meet his younger self and teach him important lessons about Pokémon training and friendship that he learned over the years.
If Merlin travels back in time, his relationship with Arthur would be very different. In the past, Arthur might not trust him at all at first. Merlin would have to prove himself all over again. With Gwen, he might be more aware of her future importance and try to protect her in a different way. And his relationship with the other knights could be completely new, as they might see him as a stranger with strange powers.
Jessie and James are the obvious ones. They are the main members of Team Rocket. Jessie could be constantly trying to outdo Ash in Pokémon battles or contests of skill. James, on the other hand, might be more conflicted about having Ash around. He could secretly admire Ash's kindness towards Pokémon and start to have second thoughts about their Team Rocket activities.
One possible plot could be that Ash initially joins Team Rocket by mistake. He gets caught up in one of their schemes and ends up traveling with them for a while. Along the way, he tries to convince them to change their ways and use their skills for good. For example, he might show them how they could use their knowledge of Pokémon capture to help rescue Pokémon in danger instead of stealing them.
If Ianto travels back in time, his relationships with the Torchwood team in his original time would be put on hold. They would be left wondering where he went. In the past, he might form new relationships. For example, he could become friends with an ancestor of one of his present - day colleagues. This would create a strange connection between the past and the present for the team when he eventually returns.
His relationship with his father Poseidon would be different. He might see a side of Poseidon that he never knew before, like when Poseidon was younger and less experienced. This could change how Percy views his father and their connection.
If Team 7 went back in time, Naruto and Sasuke's relationship could become stronger earlier. Maybe Naruto could understand Sasuke's pain from the past better and be able to prevent some of the rifts that formed between them. Sakura might also be more confident around Sasuke in the past, knowing what she knows now. Their bond as a team could be tighter as they work together to change things in the past without making big mistakes.
Their relationships would likely become stronger. They would have to rely on each other more in the unfamiliar past environment. For example, Naruto might look up to Kakashi even more as he sees how much Kakashi has grown and changed. Sasuke might be more open to the idea of teamwork as they face challenges together in the past.