There could be a scenario where Voldemort kidnaps baby Harry to use his blood for some dark ritual. This would be a really dark and intense plot. The magical protections that Lily placed on Harry might still be at work, and they could either protect Harry in Voldemort's clutches or have some unforeseen consequences. And there would surely be a great struggle between the forces of good and evil to get Harry back.
Well, it depends on the writer's take. Some might have Harry grow up in Voldemort's captivity, being taught dark magic against his will. But then he could find a way to resist and use his natural goodness to eventually escape. Or perhaps Voldemort would use Harry as a hostage to blackmail the wizarding world into submission, which would lead to a great conflict between those who want to save Harry and those who are afraid of Voldemort's threats.
In many such fanfictions, there could be a lot of different scenarios. One possibility is that the wizarding world would be in chaos. Dumbledore might lead a frantic search for baby Harry. Maybe some of the Order of the Phoenix members would try to infiltrate Voldemort's lair to rescue him. It could also be that Voldemort has some strange plan for Harry, like trying to turn him to the dark side from a very young age.
In a fanfic where Voldemort kidnaps Harry, it could lead to a lot of intense situations. Harry might be used as a bait to lure his friends into a trap. Or Voldemort could try to turn Harry to the dark side, using various forms of dark magic and psychological manipulation.
Harry could also try to reason with Voldemort. He might remind Voldemort of the prophecies and how killing him might not be in Voldemort's best interest. He could also try to appeal to any bit of humanity that might still be left in Voldemort, although that's a long shot.
A third plot twist could involve a character we least expect coming to Harry's rescue. Perhaps a Slytherin student who has been secretly against Voldemort all along. This student could have some inside knowledge about Voldemort's lair and manages to free Harry, leading to a change in the dynamic between the houses at Hogwarts.
If Orochimaru kidnaps baby Naruto in fanfiction, it would likely start a race against time for the Hidden Leaf Village to get him back. The village elders and the Third Hokage in particular would be desperate to rescue Naruto. They might send out their best ninjas, including Kakashi, to track Orochimaru down. Orochimaru, on the other hand, could be planning to raise Naruto as his own weapon, brainwashing him from a young age to be loyal only to him.
Yes, there are likely some fanfictions out there with such a wild concept. Fanfiction often explores very strange and unique ideas, and this is definitely one of the more out - there concepts. However, it's not a part of the original 'Harry Potter' canon.
Well, if Harry is captured by Voldemort in fanfiction, it could lead to some really dark and intense scenarios. Voldemort might torture Harry to get information about the resistance. Harry, on the other hand, could be secretly planning an escape while pretending to be broken. There could also be a rescue mission by his friends, which would be full of danger and drama.
In such a fanfiction, Harry might become a very different person. He could be more in tune with the Dark Arts. Maybe he would have a skewed sense of morality, influenced by Voldemort's views. He might also be more powerful in the Dark Arts but struggle with his identity as he is constantly in conflict between what he's been taught by Voldemort and his own inner goodness.
In such a fanfiction, Harry might be raised with a very different set of values. Voldemort could try to mold Harry into his own image, perhaps teaching him dark magic. But Harry might also secretly hold on to his own sense of good. For example, he could use the knowledge Voldemort gives him to ultimately turn against him.
In such a fanfiction, Grindelwald might try to use Harry to gain power over the wizarding world. He could think that Harry has some special magic or knowledge that can help him achieve his dark goals.
In such a fanfiction, Harry might be tortured for information about the Order of the Phoenix. Voldemort could try to turn Harry to the dark side, using threats against his friends.