One idea could be that Ash discovers a young and injured Mew. He takes it upon himself to nurse Mew back to health. During this time, they form a deep bond and Mew starts to teach Ash some unique Pokémon moves that are not commonly known. This new knowledge gives Ash an edge in his battles.
Well, it could start with Ash having a strange dream about Mew. When he wakes up, he finds a strange energy signal that leads him to Mew. Mew is in trouble because it has lost its memory. Ash then tries to help Mew regain its memory. As they travel together, Mew slowly remembers bits and pieces of its past, and Ash gets to learn a lot about the history of Pokémon from Mew.
Team Rocket could be the main antagonists. They might hear about Ash's encounter with Mew and try to capture Mew for their own evil plans. They could set up all sorts of traps and schemes to try and separate Ash from Mew and steal Mew away.
Well, in some 'ash mew starter fanfiction', the plot could revolve around Mew choosing Ash as its trainer. This is quite interesting because Mew is such a powerful and rare Pokémon. The story might then show how Ash and Mew form a special bond, different from the bonds he has with his other Pokémon. They could face challenges from other trainers who are jealous of Ash having Mew.
The plot could revolve around Ash and Squirtle's first days together. Squirtle might be the only Pokemon Ash has at the start. They could enter a local Pokemon competition where Squirtle has to face tough opponents. Ash would need to strategize using Squirtle's water - based moves. Along the way, they meet a mysterious trainer who gives them a tip on how to improve Squirtle's speed, which helps them in future battles.
One possible plot could be that Ash discovers a Larvitar in the wild. He decides to make it his starter Pokémon. They then embark on a journey together, facing various challenges like battles against other trainers and wild Pokémon. Larvitar evolves over time, growing stronger with Ash's guidance and training.
Well, the plot could be about Ash starting his journey with a Pidgey as his first Pokémon. Maybe he faces challenges in training it to be strong enough to take on gym battles. He could encounter other trainers who underestimate him because Pidgey is a common starter, but Ash proves them wrong as he and Pidgey grow together.
Well, it could start with Ash being in a new region where Treecko are very rare. He stumbles upon a young Treecko that is being bullied by other Pokémon. Ash steps in to protect it, and Treecko, seeing Ash's kindness, decides to join him. Their journey together focuses on exploring the unique ecosystems of this new region. Treecko has to adapt to new battle styles and opponents. Ash and Treecko also befriend a group of local Pokémon trainers who help them understand the secrets of the region. In the end, they face a powerful trainer who has a team full of strong Pokémon, and they have to use their combined skills and the knowledge they've gained to win the battle.
Perhaps in this fanfiction, Ash discovers that he has a deeper connection to Mew than he ever thought. It could involve Mew choosing Ash as a special trainer to carry out a very important mission in the Pokémon world, such as saving a certain region from a new and powerful threat. This would lead Ash to face many challenges and grow in ways he hasn't before.
The plot could start with Ash getting Riolu as his starter Pokémon instead of Pikachu. Riolu might be a bit of a troublemaker at first, not fully understanding Ash's commands. But as they journey together, they start to understand each other better.
The plot could be that Ash's powerful starter helps him quickly become a top trainer in his region. He might breeze through gym battles with ease and attract the attention of powerful trainers and organizations.
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.