I think Moon could be a great main character. She's independent and strong - willed. In the high school au, she could be the one who challenges the traditional Pokémon training methods at school. Then there's Sun, who could be her rival or partner, depending on how the story goes. There could also be some original characters created specifically for this fanfiction. For example, a new student from a far - off region who has unique Pokémon from places not seen in the original Sun and Moon games, adding a fresh perspective to the high school's Pokémon scene.
The main character could be a transfer student from Kanto. They arrive at the Alola high school with a Pikachu that has some unique abilities. This character would have to adjust to the different Pokémon and training styles in Alola. Another option is a local Alola student who has a family of Pokémon breeders. They have a special bond with a rare Pokémon from the Sun or Moon version. They get involved in school competitions and end up facing challenges that test their friendship with other students and their love for their Pokémon.
One idea could be that the main character is a new student at the high school in the Alola region. They discover a secret Pokémon club where students train their Pokémon for unique battles. Another could be a story about a rivalry between two students over who will be the top Pokémon trainer in the school. Maybe one has a team of Sun - based Pokémon and the other of Moon - based Pokémon.
Danzo could be a great antagonist in this 'naruto highschool au fanfiction'. He could be the strict school principal who enforces very strict rules and has a hidden agenda. He might not like Naruto's free - spirited nature and try to expel him. Also, Kabuto could be a student who is under Danzo's influence and causes trouble for Naruto and his friends.
Ash is the central character for sure. Then there could be some new characters created specifically for the fanfiction. They might be the ones who instigate the betrayal. For example, a mysterious trainer who has a grudge against Ash. His friends in the Alola region play a big role too. They are the ones whose reactions to the so - called betrayal by Ash form a major part of the story. Pikachu, as Ash's most loyal pokemon, is also a key character as it has to deal with the situation where Ash is being betrayed.
Obviously, Lillie is a main character. She is often the focus as the title suggests. In these fanfictions, she can be portrayed in various ways, from a shy and timid girl to a strong and fearless trainer.
A new Team Rocket - like organization could be the main antagonist. They might be after Greninja because of its unique abilities. They could try to capture Greninja to use its power for their own evil purposes, like taking over the Alola region.
Obviously, Ash is a main character. He is usually at the center of the story, going on his adventures in the Alola region.
Lillie is also a main character. She has her own story arc, especially regarding her relationship with Pokemon and her growth from being initially afraid of them to becoming more confident. And her family's secrets might also play a role in the fanfic.
The main trainer is a common character, of course. Also, popular Pokemon like Pikachu, Rowlet, and Litten often appear. They might be part of the 'harem' around the trainer. And sometimes, the Alolan regional forms of Pokemon, such as Alolan Vulpix, could also be included.
Lillie is often a popular character. Her kind nature and her growth throughout the story can be really interesting to explore in fanfiction.
The trial captains are quite popular in Pokemon Sun and Moon slash fanfiction. For example, Kiawe might be depicted in various new situations. Writers could show him having to deal with a new type of Pokemon problem or having an unexpected friendship with another character. Gladion is also popular as he has a mysterious aura, and fanfictions often delve into his past and his true motives.