One possibility is that Demando kidnaps Usagi as a way to bargain with the Sailor Guardians. He thinks that by having Usagi in his control, he can make the other Sailors do whatever he wants. Usagi, being the strong - willed character she is, would constantly resist Demando's commands and try to find any weakness in his prison or his guards to break free and rejoin her friends.
Well, maybe Demando kidnaps Usagi because he wants to use her power for his own evil plans. He might keep her in a dark, hidden lair. Usagi would be really scared at first, but then she could start to think of a way to escape using her own powers and the power of friendship. For example, she could try to send a psychic message to her friends if she has such powers in this fanfic scenario.
Perhaps Demando has some strange fascination with Usagi. He kidnaps her to make her his queen in his own little dark world. Usagi, though, is in love with Mamoru. So she would be fighting against Demando not only to escape but also to get back to Mamoru. She could start to understand Demando's motives during her captivity and try to convince him to change his ways, but also be ready to fight if he doesn't listen.
Usagi's friends would be extremely worried. They would immediately start looking for her. They might split up to cover more ground and search different areas where Demando could be hiding her. They would also use their powers to try to sense Usagi's location. For example, if one of them has a power related to sensing emotions, they could try to detect Usagi's fear or distress.
The plot could involve Usagi's sickness being related to some sort of magic or enemy plot. Since she's pregnant, her powers might be affected. Mamoru, being the loving partner, searches for a cure while also protecting Usagi. There could be a lot of emotional turmoil as Usagi is worried about the baby and Mamoru is torn between finding a solution and being by her side all the time. Eventually, with the help of their friends, they figure out what's wrong and Usagi recovers, ready to give birth to a healthy baby.
In this fanfiction plot, Theo kidnaps Lydia because he believes she can help him get revenge on someone. He takes her to a secluded location. Lydia is angry as well as frightened. She starts to play mind games with Theo, using her intelligence. Theo is taken aback by her resilience. As they interact more, Theo starts to see Lydia not just as a means to an end but as a person. This change in his perception makes him question his actions. At the same time, Lydia is constantly looking for an opportunity to send a signal to her friends so that they can come and rescue her.
Well, it could be that Nico has some dark plan. Maybe he believes Percy is the key to saving someone he loves in the Underworld. He might think that by kidnapping Percy, he can force Percy to use his powers to bring that person back to life or something like that.
The Bratva might kidnap Felicity because they think she has some valuable information. Maybe she's a tech genius and they believe she can decrypt some files that are important for their illegal business. So they snatch her away, and then Felicity has to use her wits to either escape on her own or leave clues for her friends to find her.
One possible plot could be that the other characters, like Harry and Ron, immediately start a rescue mission. They might search for clues about where Dolohov has taken Hermione. Maybe they discover that Dolohov is working for a more powerful dark wizard who wants Hermione for her knowledge of magic. Then they have to face various traps and dark spells to reach her.
Well, in such a fanfiction, Tatanga might be after Rosalina for her unique powers. Maybe he wants to use her connection to the stars to gain control over the cosmos. He could hold her captive in his dark and gloomy lair on his home planet. Rosalina, being a strong character, would try to resist and find a way to escape, perhaps using her Lumas to send out a distress signal to Mario or Luigi who would then come to her rescue.
One possibility is that Loki wants to use Harry's magical abilities for his own devious plans in the wizarding world. Maybe he thinks Harry's connection to Voldemort could be exploited to gain power over both the magical and non - magical realms.
Well, one possible plot could be that Sasuke has some sort of misunderstanding. Maybe he believes Naruto is in danger from an unseen enemy and kidnaps him to protect him. He takes Naruto to a secluded place, and at first Naruto is angry. But as they talk, they start to understand each other's motives better and their bond deepens.
One possibility is that Artemis has been misinformed. Some enemy of Percy has tricked her into thinking that Percy is a danger to the demigods. So she kidnaps him to stop him from causing harm. But as she keeps Percy captive, she slowly realizes that she has been deceived when Percy starts to explain his side of the story and the real threats he has been fighting against.