There are Lanora, the gym leader, and Ash. Lanora is likely to be a strong and respected figure in her gym. Ash, with his Pikachu and his dreams of Pokémon mastery, enters her world. Their different personalities and goals will surely lead to interesting interactions in the fanfiction.
The main characters are Lanora and Ash. Lanora, as a gym leader, has her own set of Pokémon and rules in the gym. Ash, on the other hand, is on his journey to become a Pokémon master. In this fanfiction, their paths cross and they interact, which forms the core of the story.
Obviously Ash is one of the most popular characters. And then there are the gym leaders like Brock, Misty (who also has gym - related aspects in some versions), and other gym leaders from different regions.
Well, in some ash gym leader fanfiction, there could be a story where Ash has to overcome personal challenges while facing a gym leader. Maybe he's feeling unconfident, but through his Pokémon's loyalty and his own determination, he manages to pull through. The gym leader might also have their own backstory that ties into the battle, making it more than just a fight for a badge.
One idea could be that Ash uses his unique battle style which he has developed over his journey to create a really challenging gym. He might include Pokémon from all the regions he has visited in his gym battles, making it a diverse and exciting experience for trainers. For example, he could have Pikachu lead the charge as always, but also include some of his less common Pokémon like Heracross or Gliscor.
One popular pairing is Ash x Misty. Misty is a Gym Leader and she has a long - standing relationship with Ash in the Pokémon series, so it's often explored in fanfiction.
His understanding of Pokémon could deepen further. Since he now has to design challenges for trainers, he would study Pokémon types and abilities more intensively. He might discover new strategies and combinations that he hadn't thought of during his regular journey. This could also make him more respected in the Pokémon community as a knowledgeable gym leader.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions on various topics, including Ash x Gym Leader ones. Just use the search function and type in relevant keywords.
The main characters are probably the boys who are in the gym. They could be boys from different backgrounds, with different goals for being in the gym. Some might be there to build muscle for sports, others could be there to lose weight or just to get fit. There might also be a trainer or an older boy who serves as a mentor figure among them.
I don't know the specific 'gym king story', so I can't say for sure who the main characters are. It could be the 'gym king' himself and maybe his trainer or his rival at the gym.
Obviously, Naruto would be one of the main characters since he is the leader. And the jinchuuriki would also be main characters, like Gaara who is the jinchuuriki of Shukaku.
Without reading 'the leader fanfic', it's hard to determine the main characters. However, if it's about a leader, likely there are characters that interact with the leader. These could be people from their inner circle, like a trusted friend or a family member. There may also be antagonists who oppose the leader's ideas or actions. And of course, there might be ordinary citizens who are affected by the leader's decisions and play important roles in the story as well.