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.
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.
Often, the self - inserted human characters are quite popular. These are the ones where the author imagines themselves in the Pokemon Mystery Dungeon world. They bring a sense of relatability as they experience the world from a human perspective.
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.
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.
A human artist is also a popular character in some fanfictions. This artist could be painting portraits of the animals in the circus or creating amazing set designs. Their creativity and passion for art could inspire the animals to try new things in their performances, and they would form interesting relationships with the more creative animal characters like the lemurs.
Often, the new human characters that the author creates tend to be popular. They are usually designed with unique backstories and personalities that draw readers in. For example, a human detective who comes to Toontown to solve a mystery that involves both the toon and human worlds.
Some of the more popular human characters could be those who form unexpected alliances with the main Helluva Boss characters. A human who teams up with Blitzo, for instance, and helps him with his assassination business in a way that no other demon could. This human might have a unique skill set or perspective that makes them stand out in the fanfiction community.
I think motherly Pokemon like Chansey would be likely to adopt a human. Chansey is known for its caring nature and is often seen helping injured Pokemon in Pokemon centers. It would probably see a human in need and take them in. Another one could be Blissey, which is an evolved form of Chansey and even more nurturing.
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.
Often, the new human with a mysterious backstory tends to be popular. Their mystery draws readers in as they try to figure out who this character really is and what their motives are. For example, a new human who has no memory of their past but has strange powers.