Who could be the main antagonist in a Steven Universe x Blue Diamond fanfiction?

It could be another gem who doesn't want Steven and White Diamond to form an alliance. Maybe a rogue gem who fears that their combined power would disrupt the current power balance in the gem universe.

A powerful rogue gem who has been stealing energy from other gems and growing stronger could be the main antagonist. This gem could be jealous of Blue Diamond and Yellow Diamond's power and status and aims to take them down.

There are quite a few out there. You can start by looking on popular fanfic platforms like Archive of Our Own. Some fanfics might focus on their unique relationship dynamics, exploring how Greg's down - to - earth nature could interact with Blue Diamond's complex character.

A group of Homeworld Gems who believe that Black Pearl has become too 'contaminated' by her interactions with the Crystal Gems and Steven. They see her as a threat to the traditional Gem order and send a special task force to capture or destroy her, which would make them the main antagonists as they try to stop Black Pearl from living her new life.

The main characters would be the son of Yellow Diamond, of course. Then, the Crystal Gems like Garnet, Amethyst, and Pearl would be important. They could be the ones who initially view the son with suspicion but later come to accept him. Another possible main character could be Peridot. She has knowledge of the Diamond hierarchy and could help the son understand his place in it, while also learning from him about a different perspective on the Diamonds.

One idea could be that Steven tries to understand Blue Diamond's past traumas and helps her heal. Maybe he uses his unique powers of empathy to break through her cold exterior.

It could be a corrupted Gem that has the ability to disrupt Steven's new ways of sensing the world. This Gem might be able to create illusions that confuse Steven's other senses, making it difficult for him to rely on his friends or his new powers.

The relationship in the lemon fanfiction might be a total departure from the canon. Steven, with his empathetic nature, could be the one to break through Blue Diamond's shell. Writers may use this relationship to explore themes like forgiveness and growth. They might create scenarios where Steven and Blue Diamond have to work together, leading to a development of a unique connection that we don't see in the original series.

It could be a corrupted Gem from the past that was somehow locked away and now resurfaces in the future, angry at the changes that have occurred. This Gem might not understand the new world order and wants to return things to how they were.

Tumblr also has a lot of fan - made content including fanfics about them. You can search relevant tags like #greg x blue diamond or #steven universe fanfic. There are often fanfic writers who post their works there and you might discover some hidden gems.