One popular new Ash Univa fanfiction is 'Ash's New Adventure in Univa'. It focuses on Ash exploring new regions in the Univa world, facing unique Pokémon and making new friends along the way.
FanFiction.net is also a great place to look. There are many authors who post their new Ash Univa fanfictions there. Just make sure to sort the results by the most recent to find the new ones.
Another cool new partner for Ash in fanfiction could be Riolu. Riolu is strong and has the ability to sense auras. It could learn a lot from Ash and Pikachu and grow into a powerful Lucario. This would give Ash a Pokémon with great combat skills and a unique ability that could help in battles and in understanding other Pokémon's emotions.
Begin with Ash's character. Consider his growth and development throughout the Pokemon series. You could write about a time when Ash has to face his biggest fears in a new Pokemon world. It could be a world where the rules of Pokemon battles are different, forcing him to adapt in new ways.
It could be a young girl named Lily who has just started her Pokemon journey. She has a Pikachu - like Pokemon but doesn't know how to train it properly. Ash steps in and shows her the ropes, like how to train it to use electric attacks more effectively.
Potential characters might include a new group of Pokémon thieves that Ash has to deal with. Also, there could be a local Pokémon healer who becomes an important part of the story. There might be some young Pokémon enthusiasts who look up to Ash and join him on his adventures. Another possibility is a reclusive Pokémon trainer who has some rare Pokémon and Ash tries to learn from them.
It could be his rivals. For instance, Tracey or Paul might see Ash's potential in the new region as a threat and decide to betray him. They could try to sabotage his battles by giving false tips to his opponents or stealing his battle strategies.
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.
One storyline could be about Ash finding a lost and injured Pokémon as his new partner. For example, if his new partner is a Togepi. He could nurse it back to health and in the process, form a strong bond. As Togepi grows, it could learn new moves and help Ash in gym battles, especially against fairy - type opponents.
A great Ash new Pokemon fanfiction often has a unique plot. For example, Ash could be transported to a parallel Pokemon universe where he has to learn new battle strategies. Good character development is also key. Show how Ash changes and grows in response to new challenges.