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.
First, focus on their appearance. Give them a unique look, like a special color for their hair or a distinct style of clothing. For example, an OC with multicolored hair that changes color depending on their mood. Then, think about their personality. Make them have a strong trait, like being extremely optimistic or having a sarcastic sense of humor.
The main characters are likely to be the Equestria Girls themselves. Twilight Sparkle from the human world would be a central figure as she often takes the lead in many situations. Then there are her friends like Rainbow Dash, Pinkie Pie, etc. Also, the pony versions of these characters might play important roles as they interact with their human counterparts.
Friendship is a very common theme. The OC often forms strong friendships with the Equestria Girls characters. For example, they might go through adventures together and learn the value of loyalty and trust in friendship.
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, 'Rarijack' fanfics in the MLP Equestria Girls universe can be really interesting. They often explore the relationship between Rarity and Applejack in unique ways. Some fanfics might focus on their friendship, showing how they support each other through different challenges in Canterlot High. For example, there could be a story where they have to work together on a school project and in the process, they learn more about each other's strengths and weaknesses.
There's also 'Rarijack and the Lost Friendship'. This one is a bit more emotional. It starts with a rift in their friendship due to outside influences. But as the story progresses, they realize the importance of their bond and work hard to fix it. It's a great exploration of their relationship.
One interesting plot point could be the culture shock the Equestria Girls experience when they first arrive in Equestria. They might be amazed by the magic that is so commonplace there but strange to them. Another could be their interactions with the ponies. For example, they might have to learn new ways of communication and social norms.
One possible plot could be that the Equestria Girls characters somehow get transported into the XCOM universe. They then use their unique pony powers, like Twilight's magic or Rainbow Dash's speed, to help XCOM in their fight against the alien invaders. For example, Twilight could use her magic to disrupt alien technology.
Self - discovery is also a prevalent theme. As they go on their adventures, the ninja girls learn more about their own strengths, weaknesses, and their place in Equestria. For example, a girl might discover a new power she didn't know she had while in the middle of a battle. And of course, there's the theme of honor, which is very important in ninja culture and is often reflected in how the characters behave and make decisions.