One possible antagonist could be a dark wizard who wants the baby for its own dark purposes. Maybe the baby has a unique power that the dark wizard wants to harness. Also, there could be some jealous wizards or witches in the community who are envious of the Golden Trio's fame and don't want to see them succeed in this new family venture. They might spread rumors or try to create problems for the Trio and the baby.
Well, the plot could involve the Golden Trio - Harry, Hermione, and Ron - finding an orphaned baby during their post - war adventures. They might decide to adopt it out of a sense of responsibility and love. Maybe they face challenges from the wizarding society at first as they are still quite young themselves, but they prove everyone wrong with their maturity and determination to give the baby a good life.
There could be a new dark wizard or witch emerging. This character could be jealous of Harry and Hermione's influence and see the baby as a way to get to them. They might try to harm the baby or turn it against Harry and Hermione, creating a lot of conflict and danger in the story.
In this fanfic, the social workers who are overly strict or have some biases could be antagonists. If they don't approve of Cheryl's lifestyle or think she has some flaws that make her an unfit adoptive mother, they could create a lot of obstacles for her in the adoption process. This would add drama to the story as Cheryl tries to prove herself worthy of adopting the baby girl.
It could be some of the old enemies from the Sailor Moon series who see the baby as a threat. Maybe the Death Busters, if they were still around, would want to use the baby's power for their own dark purposes.
A group of mischievous animals could also be antagonists. They might be jealous of the attention the baby gets from all the other animals in the neighborhood. So, they start playing pranks on Alvin and Brittany, like stealing the baby's toys or making a mess in their yard. But in the end, they could learn to accept the baby and become friends.
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.
It could be Orochimaru. He might be interested in the baby's unique genetic makeup, thinking he can use it to create more powerful experiments. He has always been obsessed with power and the baby's combination of Naruto and Temari's abilities would be very appealing to him.
The Originals' enemies, like the werewolves, could be antagonists. They might see the baby as a symbol of the vampires' growth and power and try to harm it. Also, some of the other vampire factions who are against the Mikaelsons could target the baby to get back at Elijah and Katherine.
There could be a mysterious dark - type Pokémon that is attracted to the unique energy of the baby. It constantly tries to get close to the baby, which poses a threat to the baby's safety. Ash and Cynthia have to fight this Pokémon off while also trying to figure out why it is so interested in their baby.
Demons might also be antagonists. They sense the new life which has a connection to powerful shadowhunters like Jem and Tessa and see it as an opportunity to strike at the shadowhunter community. They could try to possess the baby or harm it in some way.