One idea could be a human with unique skills, like being a great artist, arriving in Equestria. The ponies are fascinated by the human's different art style and the human has to learn about Equestrian art in return. For example, the human could introduce the concept of abstract art to the ponies, while learning about the magical paintings in Equestria.
A human athlete could be transported to Equestria. In Equestria, they participate in the local sports and games, but with a human twist. They might introduce new sports like skateboarding (after creating a skateboard somehow) and the ponies are both intrigued and a bit scared at first. But as they see the fun in it, they start to join in too.
Maybe there's a villain from the MLP world that follows them into the Equestria Girls world. The girls then have to team up with their Equestria Girls counterparts to defeat this villain. They could combine their different skills, like the pony Rainbow Dash's speed in the air and the Equestria Girls Rainbow Dash's skills on the track team.
MLP Equestria Girls human fanfic often explores unique storylines. It might involve the human versions of the pony characters from My Little Pony in various situations. For example, they could be dealing with high school dramas, friendships, or even some magical adventures in the human world. These fanfics can be a great way for fans to further explore the characters in a different setting.
Well, it could be about a soldier who finds himself in Equestria by some strange means. He might have to adapt to the new environment which is full of ponies with different personalities and abilities. The fanfic could explore his interactions with Twilight Sparkle and her friends, perhaps he helps them in a time of crisis or they help him understand the magic of Equestria better.
One common theme is friendship. Just like in the original My Little Pony, friendship is a central aspect. The human versions of the characters form bonds and face challenges together. Another theme is the adaptation to a new world. Since they are in the human world now, they have to adapt to human customs and society.
An old man who has a lot of wisdom from his long life in the human world. He could be a mentor figure in Equestria, guiding the ponies with his unique perspective. For example, when there are disputes among the ponies, he can offer solutions based on his human experiences of conflict resolution.
One idea could be a human arriving in Equestria and Pinkie Pie being the first to befriend them. She shows the human all the fun and unique things in Equestria like the Sugarcube Corner treats. Another could be the human and Pinkie Pie working together to plan a huge celebration for all of Equestria, bringing in elements from the human world to make it extra special.
One idea could be an OC who is a new student at Canterlot High. She has a unique power related to music, like she can make people feel different emotions through her singing. And she gets involved in a battle of the bands where there's some sort of mystery or magic influencing the competition.
The human soldier might act as a mediator between different factions in Equestria. Since they come from a different world, they could have a more objective view. They could also be a source of new ideas, like different ways of training or organizing for defense. And in some cases, they could be a bridge between the human world (if it exists in the fanfic's concept) and Equestria, facilitating trade or cultural exchange.
The characters. We already love the MLP characters, and seeing them in the context of the Equestria Rumble gives a new and exciting scenario for them. They can show off their skills and personalities in different ways.
One idea could be that the ponies in Equestria discover a lost human child in their magical forest. They decide to take the child in out of kindness. Twilight Sparkle could use her magic to create a special living space for the child. And the other ponies like Pinkie Pie would throw parties to make the child feel welcome.