One possible plot development could be the girl's attempts to escape. She might look for weaknesses in the kidnappers' routine or the place where she is held. For example, she could notice that one of the kidnappers is more lenient during a certain time of the day and try to manipulate that to her advantage.
She could pretend to be sick or injured. This might make the kidnappers lower their guard as they deal with the situation. Then she could find a chance to escape when they are distracted.
Another development could be that outside help arrives. Maybe a friend or a law enforcement agency has been tracking them down and manages to stage a rescue at a crucial moment. The story could then focus on how Beckett and Lily reintegrate into their normal lives after such a traumatic experience.
One possible plot could be the girl's struggle to escape after being sedated. She might use her wits while in captivity to find a way out, like looking for weaknesses in the kidnappers' routine. Another could be the rescue attempt by her friends or family who are desperately searching for her. They might follow small clues that lead them to where she is being held.
The plot twists. A good fanfic in this genre will have unexpected plot twists. Maybe the captor has a hidden agenda that Hermione discovers, or perhaps the rescue mission goes horribly wrong at first. These twists keep the readers engaged and eager to find out what will happen next.
In this kind of fanfic, another aspect could be how Naruto's relationship with the girl changes. At first, they might have just been friends or casual acquaintances. But now, with the pregnancy, they have to build a stronger bond. They'd need to figure out their living situation, how to support the baby financially in the ninja world, and also deal with any potential social stigma that might come with having a child out of wedlock in their society.
A third plotline could be about the captors' motives. In some fanfictions, the men holding the anime girl captive might have complex motives. It could be for some sort of power play, like they want to use her as a bargaining chip against someone else in the anime world. Or they might have a strange, misdirected affection for her and are holding her captive in an attempt to 'protect' her in their own warped way.
One great 'Hermione Held Captive' fanfic is 'The Captivity of Hermione' by an unknown author. It has an interesting plot where Hermione is held captive by a dark wizard but uses her wits to outsmart him at every turn. The story is full of suspense and the author does a great job of keeping the readers on the edge of their seats.
One plot idea could be that Percy is held captive by an ancient, forgotten sea deity who wants to use Percy's powers for its own dark purposes. Maybe this deity has the ability to manipulate water in ways that even Percy hasn't seen, and he has to find a way to outwit it using his wits and the limited power he can access while captive. Another idea is that he's held captive by a group of rogue demigods who believe Percy is a threat to their new world order. They try to brainwash him into joining their side.
There could be a more complex ending. For example, the girl, through her interactions with the kidnappers, actually helps one or more of them see the error of their ways. They then turn themselves in, and the girl is released. This ending would show the power of redemption and the human capacity for change, even in such a dark situation.
One possible plot development could be the immediate rush to get medical help. Maybe some bystanders call an ambulance and the girl is rushed to the hospital where the doctors fight to save her life.