Perhaps in the fanfiction, Madara kidnaps Sakura because he realizes her potential as a medic - nin. He wants her to heal his old wounds or maybe study her unique healing abilities to find a way to make himself invincible. He could keep her in a hidden lair and force her to perform medical experiments on him.
Well, one possible plot could be that Gaara has some misunderstanding. Maybe he believes Sakura has some knowledge or power that can help his village in some way. So, he kidnaps her to force her to share that. But then as the story unfolds, Sakura tries to make him understand that she can't help as he thinks and they start to see each other in a different light, perhaps even becoming friends in the end.
Perhaps Sakura kidnaps Sasuke because she suspects he is in danger from some unseen enemy. She believes that by taking him away from the normal routine, she can protect him. She might have some inside information about a threat to Sasuke's life. In the process, Sasuke at first is angry with her for this drastic measure, but then realizes her good intentions as she reveals what she knows.
Well, one possibility is that Itachi has some hidden motives. Maybe he believes Sakura has knowledge about something important in the ninja world, like a secret jutsu or information about an enemy. So he kidnaps her to extract that information.
One possible plot could be that Team Hebi has a vendetta against someone Sakura is associated with. Maybe they think by kidnapping her, they can use her as a bargaining chip. For example, if Sakura is close to Naruto, and Team Hebi wants something from Naruto like a powerful jutsu or access to some secret information in Konoha. They might hold Sakura hostage until Naruto complies. Another aspect could be that they are being controlled by some greater evil force that has ordered them to kidnap Sakura for some dark purpose related to her medical skills or her chakra nature. It could also be a case of misinformation where Team Hebi believes Sakura has something that she actually doesn't, like a key to a hidden treasure or a special power.
Naruto would be extremely enraged. He would vow to rescue Sakura no matter what. He would immediately start gathering his friends and form a rescue team. Sasuke, on the other hand, might initially seem more reserved but would also be determined to get Sakura back. He would use his Sharingan skills to track Madara.
The Hidden Leaf Village would surely launch a rescue mission. They would send their best ninjas, like Sasuke, Kakashi, etc. This could lead to intense battles between Madara's forces and the Leaf Village ninjas. It would be a great opportunity to show off different ninja techniques and strategies.
One possible plot twist could be that Sakura discovers a hidden weakness of Madara's during the fight. Maybe it's a chakra point that, when struck, temporarily paralyzes him, giving her an upper hand.
Perhaps Madara has some ulterior motives for kidnapping Hinata. He might want to use her as a bargaining chip against the Hidden Leaf Village. Or he could be interested in her unique abilities. In that case, the Hidden Leaf would have to decide whether to meet Madara's demands or try to outwit him to get Hinata back safely.
In this high school setting for Madara and Sakura fanfiction, Madara could be a star athlete, perhaps in martial arts. Sakura is interested in medicine and is part of the school's first - aid club. Madara gets injured during a tournament, and Sakura is the one who treats him. This is the start of their relationship. As they get to know each other better, they discover that they both have family issues that they are dealing with. They support each other through these tough times, and their relationship blossoms into a beautiful high school romance.
One possible plot twist could be that Sakura, during the time travel, accidentally alters the past in a way that instead of Madara becoming a villain, he becomes a hero. This change could completely shift the future she came from. For example, if she prevents Madara from finding certain power sources or meeting certain people who influenced his dark path, it could lead to a very different Naruto world. Maybe he would use his strength to unite the clans in a more peaceful way, and Sakura would then have to figure out how to return to her own time in this new timeline.