Another option for antagonists could be a group of rogue minions. These minions could be jealous of the attention that the new baby will get. So they team up with an old enemy of Gru's and try to disrupt the pregnancy and the family's happiness.
Perhaps a new villain emerges, someone who is jealous of Gru's transformation into a family man. This villain could target Lucy during her pregnancy, thinking that by harming her, they can break Gru. The villain might use various traps and mind - games to try and get to Lucy.
The Vicious 6 could be the antagonists. They might see Gru's preoccupation with Lucy's pregnancy as a weakness and try to take advantage of it. They could plan to kidnap Lucy to get to Gru and force him to give up his new - found family life and return to his old villainous ways.
One plot could be that Gru is overly protective of Lucy during her pregnancy. He tries to baby - proof the whole house in his own wacky way, like using his minions to create special security systems for the baby's room. Meanwhile, Lucy is still trying to keep up with her secret agent duties, which causes some comical misunderstandings between them.
The father of the baby could potentially be an antagonist if he has a different view on the pregnancy than Lucy. For example, if he wants her to have an abortion and she wants to keep the baby, he could create obstacles for her.
Rittenhouse could be antagonists. They might see the baby as a tool or a threat to their plans for controlling time. They could try to kidnap the baby to use its potential powers for their own evil purposes.
The antagonists could be dark guild members. They might hear about the special baby that Lucy and Laxus are involved with. Maybe the baby has some sort of powerful magic within it, and the dark guild wants to steal the baby for their own evil purposes. So they constantly try to attack Lucy and Laxus to get their hands on the baby.
One possible plot could be about the challenges they face as new parents. Maybe they have to balance their work with taking care of the baby. Gru, with his past of being a villain, might be worried about how his past could affect their child. Lucy, on the other hand, could be using her skills from the Anti - Villain League to keep the family safe. They might also have funny moments like when the Minions try to help with the baby but end up causing chaos.
It could be powerful fairies who have a vendetta against Lucy for being a slayer. Maybe they are the leaders of a fairy clan who see her as a threat to their existence.
It could be another guild that sees Natsu as a threat. They might find out about Lucy kidnapping Natsu and try to use the situation to their advantage. For example, they could try to steal Natsu's magic or get information out of him while he's in a vulnerable state. Another possible antagonist could be a character who has a grudge against Lucy. They might try to stop her from getting away with the kidnapping or use it as a way to get revenge on her.
A common theme is their relationship development. Many fanfictions explore how they got closer and fell in love. Another theme is family. Since they are part of a big family with the Minions and the girls, stories often revolve around how they handle family - related situations together.
The Brotherhood of Mutants could also be antagonists. They might view the pregnancy as a sign of the X - Men becoming too domesticated and vulnerable. They could launch attacks on the X - Mansion in an attempt to disrupt Rogue and Logan's new - found family situation.
Maybe there are some traditionalists in their world who don't approve of their relationship or the pregnancy. These people could be the antagonists, constantly trying to break them apart or cause problems for them.