The main characters would most likely include Ash in his new form as Victini. His Pokémon team, not just Pikachu, but also others like Bulbasaur, Charmander etc. if they are still with him. And there could be new characters introduced, like a Pokémon sage who has knowledge about Victini and can guide Ash in his new state. There might also be some rival trainers who are both envious and intrigued by Ash's transformation.
Obviously, Ash would be one of the main characters, since he's the one turning into Victini. Pikachu would also be important as Ash's most loyal Pokémon. And Victini itself could be a key character, either as a part of Ash now or as an entity that helps Ash understand his new form.
Perhaps Ash, as a Victini, would attract a lot of attention from other Pokémon and trainers. Some might see him as a symbol of hope and victory, while others could be jealous or even try to capture him for his powers. His friends, like Pikachu, might be initially confused but would eventually learn to accept this new form of Ash and help him navigate the challenges that come with being a Victini.
Obviously, Ash would be the main character since he's the one collapsing. His Pikachu would most likely be a key character as well. Pikachu is always by Ash's side and would probably be very concerned and try to help when Ash collapses.
Obviously, Ash and Erica would be the main characters. Ash is the one who undergoes the transformation, so he's central to the story. Erica is the one who causes the change, so she also plays a crucial role.
One way is through shared goals. For example, if there is a powerful and evil Pokemon causing trouble in the region. Ash wants to stop it for the sake of the Pokemon and people, and Victini wants to stop it because it threatens the balance of the Pokemon world. As they work towards this goal, they learn about each other's strengths and weaknesses. Ash might learn that Victini is afraid of certain types of attacks, and he protects it. In return, Victini uses its victory power to give Ash's Pokemon an advantage in battles. This mutual reliance and protection deepens their relationship.
The main characters would surely include Ash. In Pokemon Red, the rival character, Gary (or whatever name you choose for the rival in the game), could also play a major role. And of course, the various gym leaders from Pokemon Red. They could have different encounters with Ash, some might be friendly and help him, while others could be more challenging opponents. Also, Professor Oak might be involved, as he is connected to both Ash's world and the world of Pokemon Red in some ways.
The main character is surely Ash. He is the one who is being betrayed. Mew is another important one. It might be that Mew is the cause, directly or indirectly, of Ash's betrayal. Then, Ash's Pokémon partners are likely to be main characters too. They might be confused or forced to side against Ash. And there could be some antagonists in the story, perhaps some evil trainers or organizations who are behind the plot to make Ash look bad and get betrayed.
The main characters would surely be Ash and Mewtwo. But there could also be other Pokemon that play important roles. For example, Pikachu might have a different relationship with Ash since Ash was raised by Mewtwo. And perhaps some of Mewtwo's clones could also be involved, adding more depth to the story.
Obviously, Ash would be one of the main characters since he's the one who turns into a Pokémon. His Pokémon partners like Pikachu would also be important. They might be confused at first about Ash's transformation but then help him adapt. And if we consider the 'lemon' as something non - adult related, there could be a new character, perhaps a wise old Pokémon that has some knowledge about Ash's transformation and guides him through this strange new phase.
Gary Oak is a likely character. He has always been a rival to Ash and in fanfiction, he might betray Ash out of jealousy or a desire to be the ultimate Pokémon trainer. Another could be Misty. Maybe she gets influenced by some external force or her own insecurities and turns against Ash. Brock could also be a candidate in some stories. If he falls in love with a girl who has a vendetta against Ash, he might be forced to choose between his loyalty to Ash and his new love interest.
Maybe a powerful and evil pokemon trainer who has a vendetta against Ash. Now that Ash is in a vulnerable pokemon form, this trainer could try to capture and control him. The trainer might have some dark motives related to using Ash's unique situation to gain power in the pokemon world.