Obviously, Ash is one of the main characters. He is the trainer who gets the legendary starter. And of course, the legendary starter itself is also a main character. It has its own personality and abilities that play a big role in the story.
Well, in many fanfictions about Ash and legendary starter Pokémon, the writers often give Ash a unique bond with these Pokémon. It could be that he has to save a legendary starter from an evil organization. This not only tests his skills as a trainer but also his moral compass. He might learn new techniques or gain access to special areas in the Pokémon world because of this connection. It's a great way to expand on the original Pokémon story and give Ash more depth as a character.
One interesting storyline could be Ash getting a legendary starter that has a unique bond with him. For example, it might be able to communicate telepathically with Ash. This could lead to them having a deeper understanding of each other and facing challenges in a new way.
Perhaps an ancient evil spirit that was sealed away long ago. The hatching of the legendary starter's egg is a sign that the spirit can break free. It wants to possess the starter to regain its full power and take over the Pokemon world. This would make for a very dark and menacing antagonist, and Ash would have to use all his skills and the power of his friendship to defeat it.
In a Pokemon fanfiction with Ash and Mewtwo, it could start with Ash encountering Mewtwo in an unexpected place. Maybe in a hidden forest where Mewtwo is observing the wild Pokemon. Ash, being his curious self, tries to approach Mewtwo. Mewtwo, initially hostile, realizes Ash's pure intentions and they start an unlikely friendship. This could lead to many adventures where Ash and Mewtwo face various challenges together, like battling against a new, powerful and evil Pokemon organization.
In a fanfiction like this, the plot could revolve around the fact that the egg is the key to restoring balance in the Pokemon world. The legendary starter that hatches from it is initially weak but grows rapidly under Ash's care. However, there are forces at work that want to use the starter for their own evil gains. Ash has to team up with his friends and other Pokemon to fend off these threats. The story could also explore the relationship between Ash and the legendary starter as it grows, how they learn from each other, and how their bond becomes unbreakable.
One common theme is growth. Ash and his starter often go through significant character growth as they face different challenges. For example, they might learn important lessons about friendship and perseverance.
Often, the antagonists in these fanfictions are popular. Imagine an evil team that wants to capture the legendary starter for their own dark purposes. Their leaders, with their devious plans and menacing auras, can draw a lot of attention. Another popular character could be an old sage - like figure who has knowledge about the legendary starters and can offer guidance to the main characters.
In fanfiction, the relationship between Ash, Ho - Oh, and his starter can be very creative. Ash's starter might be a rare or unique one that has a connection to Ho - Oh's legend. Ho - Oh could see Ash's pure heart through his relationship with his starter and choose to guide them on their journey. This could lead to Ash uncovering secrets about the Pokemon world that are related to Ho - Oh and the starters' origins.
It could be a Pikachu. Since Pikachu is often associated with Ash and could be considered a special kind of 'first' pokemon for him in a different take of the story.