It could be an ancient evil that has been awakened by the news of the pregnancy. This evil entity might view the baby as a powerful force that could either be an ally or an enemy in the future. So, it tries to either destroy the pregnancy or claim the baby for its own dark designs.
Another possible antagonist could be Zelena. Jealous of Belle's happiness and the new life she's bringing into the world, Zelena could try to cause trouble. She might use her magic to create false scares or difficulties during the pregnancy, like making Belle believe there are problems with the baby when there really aren't.
Perhaps the fanfic could be about how the pregnancy changes their relationship. Belle might become more protective of Rumple, seeing him as the father of her child. Rumple, on the other hand, could struggle with his own self - worth, fearing that his past deeds will somehow taint the new life. They go through a journey of self - discovery and growth together as they await the arrival of their baby.
Elena could be an antagonist. Since she has a history with Christian, she might try to interfere with Anastasia's pregnancy, perhaps out of jealousy or a desire to maintain some control over Christian.
The main antagonists could be the same organizations they have always fought against. For example, Umbrella Corporation or any other bio - terrorist groups. These groups might see Ada's pregnancy as a weakness and try to use it against them. They could target Ada to get to Leon or try to harm the unborn child to stop Leon from interfering with their evil plans.
It could be Gabriella's over - protective father. He might think that Troy isn't ready to be a father and tries to convince Gabriella to break up with him. He believes that their pregnancy will ruin Gabriella's future and he's very strict about it, causing a lot of tension between the couple and him.
It could be some rogue ninjas who see Temari's pregnancy as a vulnerability and try to target her or Shikamaru. They might think that a pregnant Temari would be an easy target and that Shikamaru would be distracted, so they could try to carry out some evil plan against them.
One possible antagonist could be Blair. If she still has feelings for Nate, she might see Serena's pregnancy as a threat to her relationship with Nate, whether it's a real relationship or just her own feelings. So she could try to create problems between Nate and Serena during the pregnancy.
One great 'Rumple and Belle Fanfic' is 'A Different Kind of Love'. It beautifully portrays their complex relationship. The author does an amazing job of delving into Rumple's insecurities and Belle's unwavering hope. It shows how their love can overcome many obstacles, and the story has some really touching moments that will make you fall in love with their relationship all over again.
The Capitol would definitely be a main antagonist. They are always trying to control the tributes and the Hunger Games. With Katniss pregnant, they might see it as an opportunity to manipulate the situation for their own entertainment or to quell any potential uprisings. President Snow could be especially cruel in this scenario, using Katniss's pregnancy to threaten her and those she loves.
It could be some of the traditional enemies they face. For example, the Foot Clan might see this as an opportunity to target them, thinking that a pregnant April and a distracted Raph would be easier to attack.
One common theme is redemption. Often, Belle is trying to redeem Rumple from his dark ways. Another theme is love conquering all. Their love is seen as a powerful force that can change things.