A possible plotline could be that Ash is in a tournament and all his regular Pokémon are unable to compete further. So, he calls upon the strongest Pokémon, say Lugia. Lugia then uses its amazing powers to defeat all the opponents and Ash wins the tournament, which also earns him respect from all the trainers.
Another plotline could be that Ash is trying to prove himself to a group of elite trainers. He calls the strongest Pokémon, which could be Dialga. Dialga's ability to control time gives Ash an edge in battles. But with great power comes great responsibility, and Ash has to learn how to control Dialga's powers properly while also facing the envy and challenges from the other trainers.
One of the popular fanfics where Ash calls the strongest Pokémon could be those where he summons Arceus. In some fanfictions, Ash might have a special connection with Arceus, the so - called 'God of Pokémon'. This could lead to epic battles and adventures as he teams up with the most powerful being in the Pokémon universe.
A plotline could involve a special Pokemon that both Ash and Paul are interested in. They might compete to catch it, which could involve a series of challenges and battles. Or, perhaps there's a new type of Pokemon training technique that one discovers and the other tries to learn from or outdo. This could create an interesting dynamic in the fanfic.
One plotline could be that Ash uses his ability to speak to Pokemon to solve a mystery. For instance, a group of Pokemon are acting strangely, and by talking to them, he discovers that there is a hidden force affecting them. Another could be that he has to convince a powerful and angry Pokemon not to destroy a village by communicating with it on a deeper level.
A really exciting plotline could be Ash getting a chance to time - travel. He could go back to the past and meet his younger self or even go to the future to see how far he has come as a trainer. Along the way, he would face challenges related to the different time periods and the Pokemon that exist there.
A possible plotline could involve Jessie using her femdom - like influence to reform Team Rocket's goals. She could bring Ash into her plans, making him follow her lead. Ash, initially resistant, might gradually come to see the value in her ideas. This could involve them working together to solve problems in the Pokemon world in a new way, with Jessie always being the one calling the shots. Their relationship could be filled with banter and challenges as Ash tries to assert himself while still following Jessie's lead.
One possible plotline could be that Ash somehow gets merged with Lugia's power during an unexpected encounter in a mysterious place. Maybe he's trying to protect Lugia from some evil force, and in the process, a magical transformation occurs. This could lead to him having to learn how to control Lugia - like powers, such as flying and using powerful water - based attacks. Another plotline could involve Ash being transformed into a Lugia - like form and having to hide it from his friends at first, fearing their reaction.
One possible plotline could be that Ash is forced into a dress as part of a prank by Team Rocket. They might use some sort of device to make him unable to take it off easily. Another could be in a different region where there's a strange cultural tradition that requires outsiders to wear a dress in a certain situation, and Ash, being unaware, gets caught up in it. Maybe his Pokémon try to help him get out of the situation in comical ways.
One interesting plotline could be Ash encountering a new and extremely rare Pokemon that has unique abilities. This Pokemon might initially be hostile but gradually form a bond with Ash as they overcome various challenges together.
A plotline could involve a curse or a strange experiment gone wrong that causes Ash to be in a situation where he has to give birth. Or perhaps there's a parallel universe where the rules of Pokemon are different and male characters can give birth. Ash could be on a journey in this universe and have to deal with this new and unexpected situation, learning about himself and the world around him in a completely different way.
One possible plotline could be that it's set in an alternate universe where some magic or strange phenomenon causes them to become pregnant. Another could be a scientific experiment gone wrong scenario. But these are just wild speculations as such a concept is very far - fetched from the original Pokemon concept.