One interesting storyline could be a human with a special bond to a Legendary Pokemon. For example, a trainer who discovers they have an ancient connection to Mewtwo. They might go on a journey to understand this connection and in the process, face challenges from other trainers or organizations who want to use this connection for their own gain.
Another storyline could involve a human becoming a Legendary Pokemon in a strange turn of events. This could be due to a magical spell gone wrong or an experiment. The human-turned -Legendary would then have to navigate the Pokemon world with new powers and a different perspective, while also trying to find a way to turn back.
One interesting storyline could be the children having to discover and control their latent powers inherited from the legendary Pokemon. They might face challenges like being hunted by those who want to use their powers for evil.
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.
One interesting storyline could be Ash getting a legendary starter that has a unique bond with him. For example, it might be able to communicate telepathically with Ash. This could lead to them having a deeper understanding of each other and facing challenges in a new way.
Maybe a story where Ash is transported to a realm where human legendaries live. He has to navigate their complex society and politics. The human legendaries might be divided into different factions, some believing in isolation from the normal Pokémon world, while others think they should be more involved. Ash could become a mediator, trying to bring peace between these factions while also learning about the unique powers and histories of these human - like legendaries.
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.
A plot could involve a human accidentally stumbling into the hidden realm of Legendary Pokemon. There, they have to prove themselves worthy to the Pokemon and in the process, they develop a unique friendship. The human then uses this new - found relationship to bring peace between humans and Legendary Pokemon who have long been in conflict due to misunderstandings.
One common theme is friendship. Humans and Legendary Pokemon often form deep bonds of friendship in these stories. Another theme is adventure, as they usually go on exciting quests together.
Well, start with a strong concept. Imagine a world where Legendary Pokemon are hunted, and a small group of humans are trying to protect them. One of the humans forms a special bond with a Legendary, say Zekrom. The key is to build the relationship gradually. Show how the human and Zekrom learn to communicate, maybe through shared experiences or a common goal. Also, don't forget about the setting. Describe the environments where they interact, like a hidden cave filled with ancient Pokemon markings that holds a secret related to the Legendary Pokemon's power. This will make the fanfiction more immersive.
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.
One possible plotline could be Ash's discovery of his own latent legendary powers. Maybe he starts to exhibit abilities that are unique to legendary Pokemon, like controlling the weather or having an extraordinary bond with all types of Pokemon.