In these fanfictions, a very common theme is adaptation. The human who has become an anthro alicorn has to adapt to a whole new set of physical abilities, like flying and using magic. There's also the theme of cultural shock. Equestria has its own culture, and the new alicorn has to understand and adapt to it. Additionally, the theme of heroism often pops up. As they gain powers, they may be called upon to save Equestria or help its inhabitants, which is a big change from their human life.
I'm not sure about a specific title right off the bat. But you can usually find great 'human turns anthro alicorn' MLP fanfictions on websites like Fimfiction.net. Just search for the keywords 'human anthro alicorn' and you'll likely come across some really good ones. You can also check out some MLP fanfiction forums where people might recommend their favorite stories in this genre.
One common theme is self - discovery. Since the oc alicorns are often new characters in the MLP universe, they usually go through a process of finding out who they are and what their purpose is. Another theme is friendship, just like in the main MLP series. The oc alicorns form bonds with other ponies and learn valuable lessons about loyalty and kindness.
Friendship is also a big theme. Just like in the main My Little Pony series, the female alicorn OCs form friendships with other ponies. These friendships help them through tough times and are a source of support. In some fanfictions, the OC might be an outcast at first, but through friendship, they find acceptance.
One common theme is self - transformation. The character goes from being a normal human to an alicorn, which often involves a lot of internal and external changes.
One common theme is self - discovery. As Twilight becomes an alicorn, she has to figure out her new place in the world. Another theme is the power and responsibility that comes with her new form. For example, in many fanfics, she has to learn how to use her enhanced magic wisely.
Power management is another theme. Alicorn Twilight has more power, and fanfics often explore how she can control it. Some fanfics show her struggling with the magnitude of her power, while others show her using it skillfully to overcome obstacles and protect those she cares about.
One common theme is self - discovery. When a human turns into an anthro Pokemon, they have to figure out who they are in this new form. For example, they might discover new abilities or instincts that they didn't have as a human.
One popular story could be about a young girl who, through a magical accident, starts to transform into an alicorn. She discovers new powers like flight and magic as she goes through this change, and has to learn to adapt to her new form while hiding it from the non - magical world.
One common theme could be friendship among the characters in the harem. Another might be Spike's growth and development as he interacts with multiple characters in an anthro - style setting.
Friendship is a very common theme. It often shows how humans and anthro pokemon can form deep bonds. Another is adventure, as they usually go on some kind of journey together.