One plot idea could be a male human who discovers Sunset Shimmer's world by accident. Maybe he's a new student at Canterlot High and is immediately drawn to her mysterious aura. He could then help her with some sort of school project that also involves dealing with magic problems in their town.
Another plot idea is that the male human is a huge fan of Sunset Shimmer's music. He gets a chance to meet her at a concert and they strike up a conversation. From there, they start to hang out more often, and the male human shows Sunset Shimmer the human world in return for her showing him the magical side of her world. Their relationship grows as they learn more about each other's worlds.
One great 'human x sunset shimmer fanfiction' is 'A New Beginning'. It has an interesting plot where the human character helps Sunset Shimmer adjust to a new life in the human world. The relationship development between them is really engaging.
Communication is key. In the fanfiction, show them having deep conversations about their hopes, dreams, and fears. The male human can share his experiences growing up as a human, and Sunset Shimmer can talk about her life in Equestria and at Canterlot High. This open communication will make their relationship seem more real and believable as it progresses.
One idea could be that Sunset Shimmer somehow gets transported to the Naruto universe. She could use her magic skills in unique ways there. Maybe she teams up with Naruto to fight against a common enemy like an Akatsuki member who has some strange magic - like powers. They could learn from each other's combat styles and grow stronger together.
One idea could be that Sunset Shimmer has to balance her pregnancy while still dealing with her magical studies. She might face challenges from her peers who doubt her ability to continue her progress while expecting. Another plot could involve her searching for a special kind of magic to ensure a healthy pregnancy for her and the baby. And perhaps she forms a new friendship with someone who has experience in both magic and motherhood, who guides her through this new phase of her life.
A third idea is that the male OC is from a different dimension. He accidentally lands in Equestria and meets Sunset Shimmer. At first, Sunset is suspicious of him but realizes he's lost and in need of help. They embark on a journey to find a way to send him back home. Along the way, they encounter various obstacles and have to rely on each other's strengths. This adventure brings them closer together, and by the time they find a way for him to return, they have developed deep feelings for each other.
There is 'The Human and the Sunset' which delves into the relationship between a human and Sunset Shimmer. It focuses on how they overcome cultural differences, as Sunset comes from Equestria and the human from our world. The story is filled with adventures and emotional moments as they learn to co - exist and care for each other.
The theme of identity is very common. Sunset Shimmer has to figure out her new identity as a human. Love and relationships are also themes that pop up. It could be platonic love with friends or a romantic interest in someone. And the theme of exploration is there too, as she explores the human world, its culture, and its opportunities.
One idea could be that Sunset Shimmer's little brother is a new student at Canterlot High. He could struggle to fit in at first because of his sister's reputation, but then find his own group of friends through his unique talent, like being an amazing artist. Another plot could involve him getting caught up in a magical mystery where he has to use his wits to solve it and prove himself to his sister.
One idea could be a crossover with the Harry Potter universe. Sunset Shimmer could be a new student at Hogwarts, and her magical abilities from her own world could interact in interesting ways with the magic in the wizarding world. For example, her ability to transform might be mistaken for a new and strange form of Transfiguration.
Some dedicated MLP (My Little Pony) fanfiction forums might also have some good 'human x sunset shimmer' stories. These forums often have a community of passionate fans who share their works and recommendations.