One idea could be that Kagome's transformation into a Legendary Pokemon is a result of a strange encounter with a powerful Pokemon artifact in the Pokemon world. Maybe she was exploring an ancient ruin and accidentally activated a spell that merged her with the essence of a Legendary Pokemon, like Mew. This could lead to her having unique powers and abilities that no other trainer has.
In a fanfic, Naruto turning into a Pokemon might also lead to some comical situations. Imagine Naruto, now as a Pokemon, trying to communicate with his friends in Konoha. He might have to use Pokemon sounds and gestures at first, causing a lot of confusion among his comrades. But eventually, they figure out a way to understand him, and it becomes a fun adventure for everyone.
Kagome's character development could involve her learning about the responsibilities that come with being a Legendary Pokemon. In the fanfic, she might initially use her powers for her own benefit or to get back to her normal form. But as she meets other Pokemon and trainers who are in need, she starts to understand that she has a duty to protect the Pokemon world. This realization could transform her from a somewhat self - centered girl (in the sense of just wanting to go back to normal) to a selfless hero in the Pokemon world.
Another possibility is Ash becoming Lugia. Lugia is known as the guardian of the seas. As Lugia, Ash could explore the deep oceans, discover new species of Pokemon, and safeguard the marine ecosystem. He could use his psychic and flying abilities to interact with both water - and flying - type Pokemon, bringing a new era of harmony between different Pokemon types.
Well, it could be special because of its unique take on the Pokémon world. Maybe it has an interesting plot involving Kagome that no one has thought of before.
One idea could be that Naruto discovers a strange portal that transports him to the Pokemon world. Since he has his ninja skills, he quickly adapts. He might start by befriending Pikachu, as it's one of the most iconic Pokemon. His goal could be to become a Pokemon master, using his determination from being a ninja.
A fanfic could explore how Hiccup's transformation into a girl affects his friendships. Astrid might react in a complex way. At first, she could be jealous or confused, but then they could form a stronger bond. Also, Hiccup's father, Stoick, might have a hard time adjusting to his son becoming a daughter, which could add a lot of emotional depth to the story.
If Ash becomes a legendary Pokemon in a fanfic, it would change the whole Pokemon world dynamic. He might be hunted by evil organizations who want to use his power. On the other hand, he could also use his new form to protect the Pokemon world better than ever. His friends would likely have a mix of reactions, from being amazed to being worried about losing the old Ash.
Sorry, without reading it, I can't give a proper summary. But it might be about Kagome's adventures in the Pokémon world where she has some sort of legendary connection.
One interesting concept could be how the legendary Pokemon's unique powers translate into human abilities. For example, a Mewtwo as a human might have extraordinary psychic powers that manifest in ways like telekinesis and mind - reading. Another concept could be their relationships with other humans and Pokemon. They might struggle to fit in or be revered because of their 'legendary' status.
You could also make Kagome a sort of mediator between different ninja clans. Given her experience with different species and groups in her own world, she could use her diplomatic skills to ease tensions between clans in Naruto. For instance, she could help the Uchiha and the Senju clans understand each other better, which could change the course of the story in the fanfic.