Family and identity are important themes as well. Harry, who has lost his parents, now has voldenort as a sort of father figure. This changes his understanding of family and also makes him question his identity as the 'Boy Who Lived' in relation to voldenort's dark ways.
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.
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.
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.
One common theme is redemption. Severus, who has had a complex and often negative relationship with Harry in the original series, gets a chance to redeem himself by protecting and caring for Harry. It shows that he can be more than just the strict and often cruel teacher.
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. Snape, who has had a rather dark past in the original series, gets a chance to redeem himself through his relationship with Harry. He can correct the mistakes he made in the past, especially regarding his treatment of Harry.
One common theme is family. Since it's about adoption, the idea of creating a new family bond between Tony and Harry is central. They learn to support and love each other like family.
One common theme is the idea of redemption. Fenrir is often seen as a villain, and through his adoption of Harry, he may find a path to redemption. For example, in some stories, he starts to care for Harry and in the process, he changes his ways.
One common theme is family. Since Sirius is adopting Harry, it explores the idea of creating a new family unit. It often shows how they bond and become a family in their own way.
Another theme is self - discovery for Harry. With the influence of the MC, Harry gets to explore different aspects of himself. For example, he might discover new magical abilities or gain more confidence in his identity as a wizard. In some fanfictions, the MC helps Harry to look beyond what he thought was possible for himself.
One common theme is family. Since Sirius is adopting Harry, it focuses on building a new family structure for Harry, different from the one he had with the Dursleys. Another theme is protection. Sirius is always on guard to protect Harry from the threats that still lurk in the wizarding world.