The father of the baby, if he turns out to be an enemy, would be a major antagonist. He could try to manipulate Emily into stopping her revenge or use the baby as leverage to make her do things she doesn't want to do.
Victoria Grayson would be a prime antagonist. In the 'Revenge' series, she was always at odds with Emily. If Emily is pregnant, Victoria might see this as a weakness and try to use it against her. She could spread rumors or try to harm Emily in some way to stop her revenge plot.
Any of the other powerful families or individuals that Emily has targeted in her revenge plan could also be antagonists. They might see her pregnancy as an opportunity to finally take her down, thinking she'll be distracted or less capable of carrying out her plans.
The pregnancy in the Emily and Aiden fanfiction could bring out different sides of their characters. Emily, who has been so focused on revenge, might start to show a more nurturing side. Aiden could become even more protective. There could be a lot of drama as they try to keep the pregnancy a secret from their enemies. They may need to make sacrifices in their revenge plans to ensure the safety of the baby. For example, they might have to postpone certain operations or take less risky actions.
One possible scenario in this fanfiction could be that Emily discovers she's pregnant while still in the midst of her revenge plot against the Graysons. This could add a whole new layer of complexity to her plans. Maybe she initially sees the pregnancy as an obstacle, but then realizes it could also be a powerful weapon in her revenge strategy.
If Emily is pregnant in the fanfiction, their relationship could become extremely complicated. Daniel might initially be overjoyed if he loves Emily, but then doubts could start to creep in. He could wonder if the baby is part of Emily's revenge plan. For Emily, she might struggle between her love for Daniel (if it exists) and her need to continue her revenge. Their relationship would be full of mistrust and second - guessing.
In Erza's world, there could be a dark mage who wants to use the power of the unborn child for their own evil purposes. They might see the combination of Naruto's ninja abilities and Erza's magic in the child as a great source of power and will stop at nothing to get their hands on it.
One potential antagonist could be Lucifer's father. He might not approve of the union or the baby, seeing it as a disruption to his grand plans or as something that could change Lucifer in a way he doesn't want. Another could be some of the demons from Hell who see the baby as a potential threat to their power or existence if it has some sort of unique abilities.
It could be some of the hospital's board members who might not approve of their relationship and Cameron's pregnancy while working at the hospital. They could try to make things difficult for the couple.
One idea could be that Emily discovers she's pregnant just as her revenge plot against the Graysons is reaching a critical point. This unexpected pregnancy makes her question her motives and actions. She might worry about the future of the child in the midst of all the chaos and revenge. Daniel, on the other hand, could be in the dark about the pregnancy at first and his reaction when he finds out could be a major turning point in their relationship within the fanfiction.
Daniel could be a potential father. Since they have a complex relationship in the original story, it would make for an interesting development if he were the father in the fanfiction. Their relationship has had its ups and downs, and a pregnancy would add another layer of drama.
There's also the possibility that it's someone from her human side. A boy from her school who she has been secretly dating. He might not know about her mermaid side yet, and when she discovers she's pregnant, she has to figure out how to tell him and also deal with the two different worlds she belongs to.
There could also be a storyline where Emily's pregnancy makes her question her revenge motives. As she's about to bring a new life into the world, she might start to wonder if her thirst for revenge is worth it. This internal struggle could be a central part of the fanfiction, with her having to decide between her old self and the new life she's about to create.