In this fanfiction, perhaps Ash starts with a Eevee. Since Eevee can evolve into multiple forms, it would add a whole new dimension to his journey. He could face different challenges as he tries to decide which evolution path to take for Eevee, and it would also attract different kinds of Pokémon opponents.
The fanfiction might have Ash starting with a Growlithe. This would change his whole team dynamic. He'd have to deal with Growlithe's strong sense of loyalty and protectiveness from the start. Also, he might encounter different trainers who are interested in trading for his unique starter, which could lead to some interesting plot twists.
Another possibility is that an old rival of Ash's, who has always been jealous of his success, becomes the main antagonist in this fanfiction. When Ash chooses a different starter, this rival sees it as an opportunity to finally defeat him, thinking that Ash's new and untested starter will be his downfall.
If Ash had a different starter like Bulbasaur in fanfiction, his team composition would change significantly. He might focus more on grass - type Pokemon to complement Bulbasaur's abilities. His travels through different regions could be affected as well. Maybe he would be more drawn to areas with more plant - life where Bulbasaur could thrive. Also, his interactions with other trainers having fire - type starters would be more interesting due to type advantages and disadvantages.
A possible plot could be centered around the mystery of Latios. Since it's a very special Pokémon, there could be ancient secrets associated with it. Ash, with Latios as his starter, would be on a quest to uncover these secrets. Along the way, they would face other trainers who are envious of Ash having such a powerful Pokémon. Ash would have to prove that he is a worthy trainer of Latios through his skills and the bond they share.
One idea could be to have Ash start with a different type of Pokémon that is not commonly chosen in the main series, like a Skorupi. The story could revolve around the challenges he faces in training it as it has a somewhat menacing appearance and is a Poison - type, which might make some people in the Pokémon world a bit wary. This would lead to interesting interactions with other trainers and gym leaders.
Well, if it's 'Ash gets a different starter fanfiction', perhaps he gets a Bulbasaur as his starter. This would lead to him being more involved in grass - type Pokémon battles and strategies. He could end up exploring different regions in search of rare grass - type Pokémon to strengthen his team. Also, his personality might develop in a different way, as Bulbasaur has a calmer and more patient nature compared to some other starters, which could influence Ash's own temperament over time.
The plot could involve Ash and Chimchar facing a series of challenges in a new Pokémon league. They might encounter a powerful villain who has a special device that can nullify Chimchar's fire attacks. Ash then has to find a way to train Chimchar to use its other skills, like its speed and agility, to defeat the villain's Pokémon.
One possibility is that Ash discovers a young Rayquaza at the start of his journey. Maybe it's injured and Ash nurses it back to health. This could lead to a strong bond between them, and Rayquaza could become his most powerful Pokémon, helping him in battles against tough opponents like Team Rocket or other powerful trainers.
Maybe in the fanfiction, Trapinch is a rare and special Trapinch that has some kind of ancient power. Ash discovers this and has to protect Trapinch from villains who want to use its power for evil. Along the way, Ash and Trapinch form a really strong bond as they face these threats together.
Well, in this fanfiction, perhaps Ash stumbles upon a Mudkip that was abandoned by its trainer. Feeling sorry for it, Ash takes it as his starter. They start their journey together, and the Mudkip has an unusual ability to communicate with water - type Pokémon. This leads to some interesting adventures as they encounter water - based mysteries and help other Pokémon in distress. They also have to prove themselves to other trainers who doubt a Mudkip as a starter.
The plot could involve the female Ash and her Dratini exploring new regions not seen in the original series. They could discover ancient Pokémon secrets. For example, Dratini might lead Ash to a hidden cave filled with rare dragon - type Pokémon. Ash has to learn how to train Dratini in a way that suits its unique abilities. Maybe she focuses on Dratini's speed and special attacks rather than brute force. This journey of discovery and growth would be the main focus of the fanfiction.