One possible plot could be that Kaoru runs away to protect the unborn child from some sort of danger or unwanted situation in her current environment. Maybe there are people who don't approve of her pregnancy and she feels the need to escape to a place where she can raise the child in peace.
Perhaps in this fanfiction, Kaoru is kidnapped because of her special skills as a nurse. There could be an underground group that needs her medical expertise for some illegal or secretive operation. So, they abduct her to force her to work for them.
It could end with Kaoru finding a new community that accepts her and her baby. She might build a new life there and raise her child happily.
One possibility could be that Stiles runs away because he's afraid of the reactions from his friends and family. Maybe he thinks they'll be disappointed or angry. He might go to a place where no one knows him to start a new life for himself and his unborn child.
In this fanfiction, it could be that Lucy is part of a society with strict rules about pregnancy out of wedlock. She runs away pregnant to avoid the shame and punishment that would come her way. As she runs, she might meet other outcasts who support her. She then has to figure out how to survive, find medical care for her pregnancy, and create a future for herself and her baby.
Well, perhaps Kagome runs away because she's pregnant and fears the reaction of her family or friends. Maybe she wants to protect the unborn child from some sort of danger or judgment in her original community.
One plot idea could be that the kidnapper has a personal vendetta against Kaoru. Maybe Kaoru witnessed something she shouldn't have, and the kidnapper wants to keep her quiet. Another idea is that it's a case of mistaken identity, and the real target was someone else in the same hospital. A third idea could be that a deranged fan of Kaoru's kidnaps her in an attempt to make her their own, thinking they can 'protect' her from the outside world.
Well, she might be held for ransom. Maybe the kidnappers think that as a nurse, she has access to valuable medical information or drugs that they can sell on the black market.
It could be a jealous coworker. Maybe they feel that Kaoru is getting all the attention or a promotion they wanted. Another possibility is a patient who has become obsessed with Kaoru during their treatment. Or perhaps it's someone from Kaoru's past who has a grudge against her.
It could be that Naruto discovers something about the nature of his pregnancy that scares him. For example, he might find out that the child has some sort of special power that could put it in danger. So he runs away to figure out how to handle the situation without endangering the village or the child. He might seek out a hermit or an old sage to get advice on what to do.
One possible plot could be that Mal runs away to escape some kind of danger in her world. Maybe there's a powerful enemy after her and she decides the best option is to flee and find a safe haven. She might encounter new friends or allies during her journey who help her face her fears and the threats.