The plot could involve a Pokemon that was once weak or injured getting a new chance at life. Maybe it was abandoned by its trainer and then found by a kind-hearted person who nurses it back to health and trains it to become strong. This new bond could be the central theme, showing how love and care can transform a Pokemon's life.
It could be a Pokemon itself. For example, a Pikachu that has been separated from its original trainer and has to fend for itself in the wild. But then it meets a new friend, either a human or another Pokemon, who helps it start over. This Pikachu could be the focus of the story as it overcomes its past traumas and looks forward to a new life.
Well, it could be about a trainer who has failed in their previous Pokemon journey, maybe they lost a big tournament or had their Pokemon severely injured. But then they get a second chance. They might discover a new region with rare Pokemon species and use this opportunity to train differently, focusing more on the bond with their Pokemon rather than just winning.
It could be an older trainer who has been through a lot in the Pokemon world and is now getting a second chance. Maybe someone who was once a gym leader but lost their position due to some scandal and now wants to prove themselves again.
It could be about a unique take on Pokémon in a ghost - related scenario. Maybe it features a Pokémon that has some sort of spectral ability or is involved in a spooky adventure.
There could be a new rival for Ash. This rival might have a very different approach to Pokemon training, like focusing more on the beauty and grace of Pokemon rather than just battle strength.
Redemption is a very common theme. Characters often have made mistakes in the past and are seeking to make up for them in their new life. Another theme is growth. With the second chance, they grow as individuals, learning from their past experiences. For example, in 'The Great Gatsby', Gatsby is trying to recreate his past with Daisy in a new way, which involves his own growth and redemption in a sense.
One interesting plotline could be Ash starting a new adventure in a previously unexplored region. He might encounter new Pokemon species and form unique bonds with them.
It could be about Harry getting a new chance to save Sirius. Maybe in this fanfiction, the events at the Ministry of Magic unfold differently. Instead of Sirius being killed by Bellatrix, a time - turner - like device gives Harry a new opportunity to prevent his godfather's death. He could use new spells or strategies he didn't think of before.