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.
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.
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, 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.
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.
In such a fanfiction, it could be a very strange and dark scenario. Maybe Voldemort is using some sort of dark magic to control Harry and force him into this demeaning situation. It could be part of a plot to break Harry's spirit or use him as a tool in some dark ritual.
If Harry gives Voldemort the stone in fanfiction, it could be a very dark turn of events. Voldemort would likely use the stone to bring back his physical form more fully or perhaps gain some sort of immortality. However, some fanfictions might explore the idea that this act actually unites the wizarding community against Voldemort in a way that they hadn't been before. They might see Harry's sacrifice as a call to arms and fight back even more fiercely.
Well, it could be really strange. Harry might find some new perspectives on his enemies or himself. And Voldemort could get angry as he might not like how he is portrayed in some fanfictions. Maybe he'd try to change things according to what he reads.
If Harry Potter was adopted by Voldemort in fanfiction, it would be a very strange and complex situation. Voldemort is a very evil character, but he might see Harry as a tool or an heir. Harry could be exposed to the darkest magic and the inner workings of the Death Eaters. However, Harry's own strong will and the influence of his parents' sacrifice might still shine through, leading to a possible rebellion against Voldemort later on.
If Voldemort gets custody of Harry in fanfiction, it would be a huge deviation from the original story. Harry would probably be exposed to a lot of dark and cruel things. Voldemort could try to break Harry's spirit and make him abandon his values. There might be a struggle within Harry between the good he has been taught and the evil that Voldemort represents. And the wizarding world would be in even more chaos as Voldemort would have more control over the one person who was seen as the hope to defeat him.