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.
You can start by looking on fanfiction.net. It has a large collection of Harry Potter fan fictions, and there are likely quite a few 'Snape adopts Harry' ones in there. Just use the search function and type in the relevant keywords.
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 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.
In this fan fiction, Harry's development is likely to be quite different from the original series. He may start to question the black - and - white view of good and evil he had before. With Snape's intervention in his life, he might see the complexity of people more clearly. At Bloor's, he'll be exposed to a diverse range of characters and situations. This will force him to grow up faster and become more adaptable. He may also develop a more in - depth understanding of magic as Bloor's might have different magical traditions than Hogwarts, and he'll have to learn and adapt to them.
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.
In this fan fiction, Snape could save Harry from Voldemort's followers who are after him. The blood adoption might be a way to give Harry a new family connection. Snape, having complex feelings for Harry's mother, might see this as a way to fulfill a promise or a way to atone for past actions. He could then teach Harry some of his more advanced potions knowledge and help him develop his occlumency skills better.
One popular one is 'A Father's Love'. In this fanfic, Severus discovers Harry's abuse and takes him under his wing. He teaches Harry potions and helps him deal with the trauma of his past in a very heart - warming way.
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 interesting plot point could be Snape's internal struggle as he decides to save Harry. He has his own complex history with Harry's parents, so having to put aside his grudges and protect the boy adds a lot of depth. Another might be how Harry reacts to being adopted by Snape. Does he initially resist or is he secretly glad to have someone who truly cares in this new version of the story? Also, the way Snape has to hide this new relationship from the rest of the wizarding world to protect Harry from potential enemies or those who might not understand his motives.