Well, transformation is a frequently seen theme. The Diamond OCs might start off as one way but change throughout the story, either in terms of their physical form or their beliefs. Also, family and heritage play a role. Since the Diamonds have a complex family structure in 'Steven Universe', the OCs are often related to this in some way, and exploring their family ties and heritage can be a big part of the fanfiction.
One common theme is self - discovery. The OC often has to figure out who they are in the complex world of the Diamonds. Another theme is friendship, as they usually form bonds with the existing characters.
A major theme is power and its implications. The Diamond OCs often have unique powers, and the fanfictions explore how they use or misuse these powers. There's also the theme of acceptance. They may be different from the regular characters, and the stories show how they are either accepted or rejected. For example, some OCs face discrimination at first because of their differences but then find a place where they are welcomed.
One common theme is redemption. Since the Diamonds were initially antagonists, many fanfictions focus on Red Diamond seeking redemption for past actions. Another theme is self - discovery. Red Diamond often has to figure out its own identity outside of the Diamond Authority. And friendship is also a theme, like forming bonds with the Crystal Gems or other characters.
One common theme is self - discovery. Gem OCs often have to figure out who they are in the context of the Steven Universe world. For example, they might be different from the known gem types and have to learn about their own powers and purpose.
One common theme is self - discovery. The male oc often has to figure out his place in the world of Steven Universe, whether he's a gem, a human - gem hybrid, or something else entirely. Another theme is friendship. He forms bonds with the main characters like Steven, Garnet, Pearl, and Amethyst. For example, he might learn valuable lessons from them about love and acceptance.
One idea could be an OC Diamond who has different powers compared to the known Diamonds. For example, the ability to control time in a limited way. This could create interesting storylines where the OC Diamond tries to fix past mistakes within the Steven Universe world.
Power and responsibility is also a theme. Given that Steven has unique powers and Blue Diamond has her own vast power and influence. Fanfictions often explore how they use or should use their powers and the responsibilities that come with them. In some stories, they work together to solve problems that require both of their powers and the right mindset to take on the associated responsibilities.
A major theme is often power. As Pink Diamond, Steven has a different level of power and influence. Fanfictions might explore how he uses or misuses this power. Also, relationships are a big theme. His relationships with the Crystal Gems, his human friends, and even his enemies might change because of his new identity. For instance, his relationship with Garnet could be affected as she was made in part by Pink Diamond. There could be a lot of emotional turmoil and growth in these relationships.
In fanfiction, Black Diamond's story can be used to explore themes like redemption and forgiveness. If she was once a tyrant, her journey towards becoming a better being can be a powerful narrative. It can also show how the other characters in the Steven Universe world react to her change, whether they are skeptical or accepting. This can create interesting character dynamics.
In Steven Universe fanfiction, Black Diamond is often depicted as a very powerful and mysterious character. Some fanfictions might explore her past, her relationship with the other Diamonds, and how she might interact with the main characters like Steven. For example, she could be portrayed as a reformed villain who is trying to make amends for her past actions.
One popular 'Steven Universe Diamond OC Fanfiction' is 'The Diamond's New Ally'. It has an interesting plot where the OC has unique powers that catch the attention of the Diamonds. Another great one is 'A Diamond's Redemption', which focuses on an OC helping a Diamond to change for the better.
One common plot element is the exploration of Blue Diamond's past through her interaction with Steven. Another could be a situation where they are forced to rely on each other in a difficult situation. For example, they might be stuck in an alien environment together.