In a fanfiction where Ash starts in a different region, for example, Sinnoh. He could start with a Pokémon native to Sinnoh like Piplup. His adventure would be shaped by the mythology and legends of Sinnoh. He might get involved in the search for the Legendary Pokémon related to the creation of the Sinnoh region. This would not only add a new layer of mystery to his journey but also expose him to different kinds of Pokémon trainers and their beliefs. His relationships with his Pokémon would also be influenced by the Sinnoh - specific Pokéballs and items available in the region.
You can make it unique by changing the setting. For instance, if Ash starts with a Bulbasaur in a post - apocalyptic world where most Pokemon are scarce. This would force him to find new ways to train and care for his Bulbasaur, and also deal with other survivors who might be jealous or desperate for his Pokemon. It would be a completely different dynamic from the original series.
One possible plotline could be Ash starting his journey in Sinnoh and quickly befriending a rare Pokémon that is shunned by the local trainers. He then has to prove the Pokémon's worth. For example, it could be a shiny Zubat that is thought to bring bad luck. Ash, with his determination, shows everyone that it can be a powerful and loyal partner.
Well, consider Ash starting in the Hoenn region in a fanfiction. The Pokémon in Hoenn are known for their diverse abilities and forms. His Pokémon from other regions might feel a bit out of place at first. But as they explore Hoenn together, they would learn to adapt. His relationship with his Pokémon could become more collaborative as they all face new challenges. For instance, his Pikachu might have to deal with stronger Electric - type Pokémon in Hoenn, which would make it rely more on Ash for training and support. His other Pokémon would also have to learn new techniques to compete, and this shared struggle would deepen their bond with Ash.
A plotline might be that Latios is from a different dimension or time, and it has come to Ash's world for a specific purpose. Ash gets involved in this mission, and together they have to face powerful enemies. This could introduce new Pokémon species from other dimensions and new battle strategies that Ash has to learn to keep up with the challenges.
Perhaps in this new region, Ash discovers a powerful new Pokemon that others want to control. His friends, fearing the power of this Pokemon, betray him to protect the region. They might think that Ash is being too reckless with this new discovery and that it could lead to destruction. It could also be that there's a prophecy in the new region that Ash is somehow involved in, and his friends misinterpret it and believe he's the cause of potential harm.
Well, in many 'Ash starts with Gible' fanfictions, the unique bond between Ash and Gible is a big element. Gible is often portrayed as a very loyal Pokémon to Ash from the start. Another unique thing is how Gible's evolution line can be explored in relation to Ash's journey.
Perhaps it's a story where Ash and Froakie form an even deeper bond than in the original series. They might go on a quest to find a rare Pokemon that only Froakie can sense, and along the way, Ash learns more about Froakie's past and its potential. Froakie could also teach Ash some new strategies in battles that help him become a better trainer overall.
The plot might involve Ash starting his journey all over again, but this time with a Charizard as his very first Pokémon. Since Charizard is a powerful and somewhat stubborn Pokémon, Ash would have to learn how to handle it right from the start. He could face challenges like other trainers trying to steal Charizard because of its rarity. Ash would have to prove his worth as a trainer and his connection with Charizard to keep it by his side.
Well, it could be about Ash starting his journey with a Ralts. Maybe Ralts is a special one that has unique powers. Ash and Ralts could go through various gym battles together, with Ralts evolving at crucial moments to help Ash win. They might also face some tough opponents who are after Ralts' power.
The plot might involve Ash's Dratini evolving quickly due to their unique connection. It could also have elements of Ash trying to prove that Dratini can be a very powerful Pokémon from the start. He might enter it into Pokémon contests and battles, showing off its unique moves and abilities.