Another option is that it's a human who has somehow discovered the existence of Amethyst and the other Gems. This human could be a mad scientist type who wants to study Amethyst's unique gemstone and abilities. He or she might not understand the full implications of what they're doing and just see Amethyst as an interesting specimen to experiment on.
Well, in such a fanfiction, the other Crystal Gems might go on a frantic search for Amethyst. They could face many challenges along the way, like dealing with new enemies or having to make difficult choices to get her back.
Perhaps some remnants of Homeworld's military that still hold a grudge against the Crystal Gems. They might think that by kidnapping Amethyst, they can force the Gems to stop their activities on Earth or give up some valuable information.
Well, in such a fanfiction, the other characters like Steven and the Crystal Gems would likely go on a rescue mission. They'd use their powers to track her down. Steven might use his shield to protect them during the search, and Pearl could use her spear skills. Garnet would probably be leading the way with her future vision to find Amethyst as quickly as possible.
In Steven Universe fanfiction, the relationship between Steven and Amethyst can be really interesting. They are both very different characters. Steven is kind - hearted and has a strong sense of justice, while Amethyst is more of a free - spirited and somewhat rebellious character. In some fanfictions, their relationship might develop into a deep friendship where they support each other through different challenges. For example, Steven could help Amethyst come to terms with her insecurities about being a 'lesser' gem compared to the others.
Adventure is also a common theme. They go on different quests or face various threats together. This could be something like exploring an ancient gem ruin on Earth or fighting off a new enemy. The theme of acceptance is important too. Accepting each other's flaws and differences. Amethyst accepting Steven's sometimes naive view of the world, and Steven accepting Amethyst's wilder side.
Well, it's very possible. 'Steven Universe' has a huge fan base, and fanfiction writers love to explore different and often extreme scenarios. Kidnapping can be a plot device to create drama, tension, and character development. To find such a fanfiction, you could also search on Tumblr, as some fans might share links or excerpts there. Just be sure to check the tags and ratings to make sure it's appropriate for you.
There might be such a fanfic. The 'Steven Universe' fandom is quite large and creative. However, it's also possible that it doesn't exist. You could try searching on popular fanfic websites like Archive of Our Own or FanFiction.net to see if there's a story with this concept.
A common theme is innocence. Since she's a baby amethyst, the fanfictions often explore her naivete and how she discovers the world around her. Another theme is growth. It shows how she develops her gem powers and her personality over time. Also, the relationship with the Crystal Gems is a big theme, like how they protect and guide her.
One great young Amethyst fanfiction could be about her early days of training. It might explore how she learned to control her powers and interact with the other Gems. For example, a story could show her struggling with a new form of attack but finally mastering it with the help of Pearl.