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.
The relationship can develop through shared experiences. For example, if they face a tough battle together and have to rely on each other's skills to win. Ash could learn about Treecko's unique needs and habits, like what kind of food it prefers or the best environment for it to rest. This shows his care for Treecko.
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.
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, a Treecko fanfic might focus on its relationship with its trainer. For example, it could tell the story of a young trainer who chooses Treecko as their starter. They go through various adventures together, with Treecko evolving and becoming stronger over time. It could also include how they communicate and understand each other's feelings.
One possible plot could be that Ash discovers a Larvitar in a mysterious cave. The Larvitar is injured and Ash decides to take care of it. As they journey together, Larvitar starts to grow stronger and they face various challenges in Pokemon battles. Eventually, Larvitar evolves into Pupitar and then Tyranitar, becoming one of Ash's strongest Pokemon.
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.
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 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.