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.
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.
You can start by looking on fanfiction platforms like Archive of Our Own (AO3). It has a vast collection of different fanfictions, and you can use the search function to specifically look for 'human turns into alicorn' stories. There are likely to be many different takes on this concept there.
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 - transformation. The character goes from being a normal human to an alicorn, which often involves a lot of internal and external changes.
One possible scenario could be that Pikachu is exposed to a strange type of energy. This energy mutates its genetic structure, slowly transforming it into a human form. At first, Pikachu might be confused and scared, not understanding its new body. But as time passes, it starts to learn about human ways, like walking on two legs and using its hands to pick things up.
It could be an ordinary person, like a young student who was always curious about the magical world of Faust Alicorns. Maybe they accidentally stumbled upon a magic spell or artifact that caused the transformation.
Well, perhaps the human is turned into a Faust Alicorn in a strange accident involving some ancient magic. At first, they are terrified because they look so different. But then they start to discover the beauty and power of being an Alicorn. They could go on a journey to find out why this happened to them, meeting other magical creatures along the way who either help or hinder them in their quest.
One way a human could 'turn into' Zelda fanfiction is through creative writing. If a person is deeply inspired by the Zelda universe, they can start by imagining themselves as a character within it. For example, they could write about waking up in Hyrule, with all its unique landscapes and creatures. They might describe their experiences, like facing off against Bokoblins or exploring ancient dungeons. By using vivid details and elements from the Zelda games, they can create a fanfiction that is centered around their 'human' self in the Zelda world.
One idea could be that Optimus Prime turns into a human mechanic. He uses his knowledge of machinery from his days as a Cybertronian to revolutionize car repair in a small town. People are amazed by his skills and he secretly uses his new form to keep an eye out for any Decepticon threats.