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.
Lugia is a favorite too. Its majestic appearance and role as a guardian of the seas make it great for fanfiction. A human could be a sailor who gets lost at sea and is rescued by Lugia. From there, a story of friendship and adventure could unfold as they work together to protect the ocean from various threats.
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.
There are also original characters created by fans. These characters are often designed to have a unique backstory that ties them to Legendary Pokemon. For example, a character who was orphaned by a battle between two Legendary Pokemon and now has a vendetta against one of them, or a character who has a prophetic dream about a Legendary Pokemon and goes on a journey to find it.
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 most popular has to be Giratina. Its other - worldly and somewhat menacing appearance can be made into humorous situations. For example, Giratina getting scared of a Caterpie that crawls on it in a fanfiction. Ho - Oh is also popular. Its association with legend and beauty can be turned on its head. Picture Ho - Oh losing a feather and chasing a little Rattata that stole it all over the place. And Dialga, with its time - controlling abilities, can be in some really funny time - loop situations in humor fanfiction, like repeating the same embarrassing moment over and over again.
Maybe a story about a human who accidentally stumbles into the hidden realm of Legendary Pokemon. There, they form a friendship with a Legendary that is an outcast among its kind. Together, they try to change the perception of the outcast Legendary in its own community while also finding a way for the human to return home.
Another theme is the power of friendship. The female legendary Pokemon often starts off as a powerful and somewhat aloof being. But through her interactions with Ash, she learns about the value of friendship. They then go on to face powerful enemies together, relying on their friendship to overcome difficulties. This theme is well - loved as it shows how even the most powerful Pokemon can benefit from human friendship.
One of the popular pairings is Ash and Pikachu with a Legendary Pokemon like Mewtwo. They could form an unlikely alliance to fight against a common enemy. Another could be Ash and a female trainer along with a Legendary Pokemon, like Ash, Misty and Lugia. Their combined skills and the power of the Legendary Pokemon make for an interesting dynamic.
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.
Often, the antagonists in these fanfictions are popular. Imagine an evil team that wants to capture the legendary starter for their own dark purposes. Their leaders, with their devious plans and menacing auras, can draw a lot of attention. Another popular character could be an old sage - like figure who has knowledge about the legendary starters and can offer guidance to the main characters.
Giratina is also quite popular. Its 'banished' status in the Pokemon lore gives it a lot of depth. As a human in fanfic, it can be a brooding and misunderstood character. People are drawn to the idea of exploring its redemption arc or its unique view of the world, being from the Distortion World.