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.
Ash is the main human character. The legendary starter is the other key character. But there could also be other Pokemon that Ash already has in his team that interact with the legendary starter. For example, Pikachu might have an interesting relationship with the new legendary starter. Maybe they start off not getting along but then become friends as they face challenges together. Also, there could be some side characters like a wise old Pokemon trainer who gives Ash advice on how to train his legendary starter.
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.
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.
Obviously, Ash is one of the main characters. Since it's about him being a legendary Pokemon in this fanfiction, he's central to the story.
The villains in the fanfiction can also be considered main characters in a sense. They might be after the power of the legendary Pokemon. There could be a team of bad guys who are trying to capture and control a Groudon or a Kyogre to cause chaos in the Pokemon world, and Ash has to stop them. Their actions and plans create the conflict that Ash has to overcome in the story.
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.
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 of the Legendary Pokemon could be Giratina. Despite its somewhat dark and otherworldly nature, Giratina might be intrigued by Ash's light - heartedness and his ability to make friends with all kinds of Pokemon. Dialga and Palkia could also be part of the harem. Dialga, with its control over time, might see Ash as an important factor in the future of the Pokemon world. Palkia, in charge of space, could be interested in how Ash navigates different regions and spaces in his journey. And don't forget about Ho - Oh. Ho - Oh is a symbol of hope and might see Ash as a bringer of hope in the Pokemon world, thus joining his harem.
Arceus is quite popular. Given that it's considered the creator of the Pokemon universe in the official lore, it often has a significant role in fanfictions. Mewtwo is also very common. Its powerful psychic abilities and complex backstory make it a favorite for fanfic writers to explore. Another popular one is Lugia. With its majestic appearance and its connection to the sea, it's often a central figure in many stories.
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.
Well, obviously Ash is the main character. But in many such fanfictions, his Pokemon like Pikachu are also very important. They often play a crucial role in helping Ash handle his godlike or legendary powers. Sometimes, other trainers like Misty or Brock might also be part of the story, providing support or adding some comedic relief.