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.
Mario would be a likely candidate. He's always been the hero in the Mushroom Kingdom and has a lot of experience dealing with villains like Tatanga. He could use his jumping skills and power - ups to make his way to Tatanga's lair and rescue Rosalina.
Well, one possible plot could be that Naruto somehow gets transported to the Mario universe where he meets Rosalina. They could start off as strangers, but then Naruto's determination and kindness draw Rosalina's interest. Maybe they team up to face a common threat that is endangering both the ninja world and the Mario universe.
One possible plot could be that Mario saves Rosalina from a dangerous situation in space. In the heat of the moment, after the rescue, they share a kiss. It could be a sign of their deepening connection and gratitude.
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.
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.
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.
A fanfic could also focus on a more emotional side. Maybe Luma gets lost, and Rosalina has to search everywhere for it. This would show her deep attachment to Luma and how she would do anything to get it back. During the search, she could reminisce about all the times they spent together, from stargazing to playing among the stars.
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.