Perhaps Voldenort adopts Harry thinking he can use Harry's power for his own evil purposes. But then it turns out that by being close to Harry, Voldenort's own dark magic starts to backfire on him. Harry's presence could be like a catalyst that makes Voldenort's dark plans fall apart in unexpected ways. For example, spells he casts go wrong because of Harry's latent magic interfering.
A really interesting plot twist could be that Voldenort discovers that by adopting Harry, he has unknowingly set in motion a prophecy that will lead to his own downfall. The act of taking Harry from the Dursleys could have been the start of a chain of events that he couldn't foresee. Maybe Harry, while growing up with Voldenort, starts to form his own alliances and plans to take down Voldenort from the inside, using the knowledge he gains about the dark wizard's ways.
One possible plot twist could be that Voldenort adopts Harry with the intention of turning him into a dark wizard, but Harry's inherent goodness starts to change Voldenort instead. Maybe Harry shows Voldenort kindness that he has never experienced before, leading to a shift in Voldenort's character.
I'm not sure about specific fan fictions with this exact plot. But you can try searching on fan - fiction - specific websites like Archive of Our Own or FanFiction.net. Just use the keywords 'Voldenort adopts Harry from Dursleys' in their search bars.
One common theme is redemption. The idea that voldenort can be redeemed through his relationship with Harry. It gives a new perspective on his character.
In this fan fiction, Snape might adopt Harry because he realizes that Harry has a lot of potential that is being stifled at the Dursleys. He could take Harry to a secret location and train him not only in magic but also in self - defense and survival skills. Snape would have to deal with his own complex feelings towards Harry, as he has both resentment and a sense of obligation. And Harry would have to adjust to living with Snape, who is not exactly the warmest person. It could be a story of growth and understanding between the two.
There's also 'The Unlikely Bond'. This fan fiction explores how voldenort's decision to adopt Harry changes the course of the entire wizarding war. It has some great character development for both voldenort and Harry as they navigate their new relationship.
Well, perhaps in the fan fiction, Severus saves Harry from the Dursleys but then has to deal with the consequences of going against Dumbledore's plan. Dumbledore might have had a reason for leaving Harry with the Dursleys, and Severus' actions could set off a chain of events that changes the whole wizarding world. Also, Severus could find out that the Dursleys were part of a much larger conspiracy against the wizarding world, and by saving Harry, he uncovers this plot.
Perhaps Severus, while rescuing Harry, stumbles upon a hidden connection between the Dursleys and the Death Eaters. This would add a whole new layer of danger and mystery. He might have to fight off some of his former allies to get Harry to safety. It could also lead to a change in Severus' perception of Harry as he realizes the boy has been in more danger all along than just from Voldemort.
Harry might become more reserved and cautious at first. Growing up with Snape, who is not as openly affectionate as others, would make him more self - reliant. He'd also likely become more skilled in magic quicker, as Snape is a very talented wizard.
One big challenge is their pre - existing relationship. They've had a lot of conflicts in school. Snape has been rather harsh on Harry, so they need to overcome that animosity. Also, Snape has to deal with Harry's trauma from the Dursleys. He needs to help Harry heal and grow in a positive way, which is not easy for someone as emotionally reserved as Snape.
One possible plot twist could be that Snape discovers some hidden magic in Harry that he didn't expect. Maybe a power that's related to the Potters but also has a connection to Snape's own family. Another twist could be that the other Potter family members don't approve of Snape adopting Harry, leading to a family feud within the wizarding world. And perhaps, there could be a dark force that tries to use Snape's new relationship with Harry against them.
Maybe Severus discovers some dark magic plot that involves the Dursleys harming Harry in a more serious way. So, he intervenes just in time. He could use his skills in potions and magic to subdue the Dursleys if they resist, and then take Harry to a safe place, like his own secret hideout or a friendly wizard's home.