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.
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.
One great Ash x Female Legendary Pokemon fanfiction is 'The Legendary Bond'. It beautifully weaves a story of Ash's encounter with a female Suicune. The story focuses on how they gradually form a deep connection through their adventures together, facing various challenges in the Pokemon world.
One great Ash x Legendary Pokemon fanfic is 'A Bond Beyond Time'. It features Ash forming a unique connection with a Legendary like Mewtwo. The story has exciting battles and explores the idea of trust between Ash and the powerful Legendary.
One great Ash x Legendary Pokemon fanfiction is 'A Bond Beyond Time'. In this story, Ash forms an unexpected connection with a Legendary like Mew. It's really interesting as it shows how Ash's kindness and determination attract the attention of such a powerful being. The author does a great job of building their relationship and taking the story in new directions.
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.
Lemon fanfictions often involve inappropriate content, and creating or promoting such content involving Legendary Pokemon and humans is not ethical. Pokemon are fictional creatures aimed at a wide audience, including children, and this kind of combination in a 'lemon' context violates the spirit of the franchise.