There's also 'Legendary Pokemon: The Forbidden TF'. This fanfiction delves into a darker side of pokemon transformation. It involves an ancient spell that forces legendary pokemon to change forms, leading to a series of events that endanger the pokemon world. It's really exciting to read as it unfolds the mystery behind the transformation.
I really like the fanfic 'The Legendary's New Form'. It shows how the legendary pokemon adapt to their human forms in a modern human society. It has some really cool action scenes and the relationships between the characters, both human and pokemon - turned - human, are very engaging.
One possible theme could be friendship. For example, a human and a Legendary Pokemon form an unlikely bond and help each other through difficult times. Maybe the human is lost in a dangerous Pokemon territory and the Legendary Pokemon guides them out.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. These platforms have a wide variety of fanfictions related to Ash and Legendary Pokemon. Just use their search functions and type in relevant keywords.
Articuno, Zapdos, and Moltres are quite common. Their elemental powers and the mystery surrounding them make for great fanfiction material. Ash might encounter them during his travels and have to either help them or face off against them in some way.
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.
Mewtwo is also very popular. Given its origin as a genetically - engineered Pokemon, a human could interact with it in many ways. Maybe a human scientist wants to study Mewtwo further, or a young trainer tries to befriend Mewtwo and help it come to terms with its existence and powers.
I recommend the following Pokémon novels to you. They all have legendary Pokémon!
1. "Elf: The Opening Ambush Hunter": The protagonist's first Pokémon was a small fire dragon.
2. [Pokémon: Lightning Bird at the beginning of the game: The legendary Pokémon Lightning Bird was drawn at the beginning of the game.]
3. "Musashi of the Elves": Musashi and his Abbot are also one of the classic characters in elf novels.
4. [Ten Artifacts of Pokémon Evolution]: There are divine beasts like the Three Pillar King and the Hell Dragon.
I hope you like my recommendation. Muah ~
There are also fanfictions where Ash catches Rayquaza. This could be set during a time when the sky is in chaos due to some dark energy. Rayquaza is drawn to Ash because of his pure heart and determination. Ash, with his usual courage, teams up with his pokemon to assist Rayquaza in restoring balance. As a result, Rayquaza allows Ash to catch it.