A prevalent theme is the transformation of the characters. The girl might become stronger and more resourceful due to her situation. The obsessed guy could either realize the error of his ways or descend further into his obsession as the story progresses.
Often, the theme of rescue is present. It could be the girl trying to rescue herself or her friends and family attempting to rescue her. Also, there can be a theme of psychological manipulation as the obsessed guy may use various tactics to control the girl.
Perhaps the obsessed guy has a change of heart. He realizes his actions are wrong and lets the girl go. But this ending often comes with a complex set of emotions and consequences for both characters as they try to make sense of what has happened.
Well, often in these stories, the guy starts as a bit of a stalker - not in a creepy way though. He'll find out her daily routine and 'accidentally' bump into her a lot. Then there's the plot where he saves the girl from some sort of trouble, which makes her see him in a new light. Also, there's the scenario where the guy writes her love letters or poems to express his obsession in a more romantic way.
Common themes include the girl's attempts to outwit the kidnapper. She might use her intelligence or knowledge to gain an advantage. For example, if she's good at technology, she could try to use any devices around to call for help. Another theme is the idea of hope. Despite being in a very bad situation, the girl holds on to hope that she will be rescued. And there's also the theme of the kidnapper's lair. The description of where she is held captive, whether it's a dirty basement, an old warehouse, or a hidden cabin in the woods, which adds to the overall atmosphere of the story.
A frequent theme is self - discovery. Through her obsession, the girl may find out more about herself, like her own strengths and weaknesses. She might also discover new interests that are related to the person she's obsessed with. For instance, if the object of her obsession is a musician, she may start learning to play an instrument.
One common theme is the struggle for survival. The kidnapped girl has to find ways to stay alive in a dangerous situation. Another theme is the fight for freedom. She tries to escape from the kidnapper's clutches. Also, there's often the theme of hope. Despite the terrifying circumstances, the girl holds on to the hope of being rescued or escaping on her own.
One common theme is the idea of the forbidden or unexpected attraction. Sasori is a villainous character, and Sakura is a hero - like figure, so their relationship is against the normal moral boundaries in the Naruto universe. Another theme could be redemption. Maybe Sasori's obsession with Sakura leads him to question his own evil ways and seek some form of redemption. Also, there's the theme of power dynamics. Sasori is very powerful with his puppets, while Sakura has her own strength in combat and medical ninjutsu, and the fanfic could explore how their powers interact in the context of his obsession.
Another theme is redemption. Sasuke may feel that by being with Sakura, he can redeem himself for his past wrongdoings. He realizes that she has always seen the good in him, and his obsession is a way to hold on to that goodness. So the fanfics often explore how his relationship with Sakura can help him become a better person.
One common problem is the ethical aspect. Kidnapping is a serious crime and presenting it in a way that might be romanticized in fanfiction is not okay. It can give wrong ideas about relationships and boundaries.
Typically, themes might include rescue and heroism. There could be a character or a group of characters trying to save Alexis from the kidnappers.
One common theme could be the rescue or escape of the kidnapped pregnant character. Another might be the psychological struggle of the character during the ordeal.