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.
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.
He would become more nurturing. Usually, Severus is seen as cold and aloof, but with Harry in his care, he'd have to show more warmth. He might still be strict, but it would be out of love for Harry's well - being rather than just being his usual harsh self.
The two main characters are obviously Severus Snape and Harry Potter. Severus is the one who adopts Harry, changing from his usually cold and aloof self to a more caring and protective figure. Harry is the abused child who gets a new chance at a better life under Severus's care.
One possible plot could be that Severus discovers the extent of Harry's abuse at the Dursleys. He decides to take Harry in out of a sense of duty or perhaps a hidden soft spot for the boy. He then has to teach Harry about magic in a more personal and nurturing way, different from Hogwarts. They might also face opposition from the wizarding community who question Severus' motives.
One interesting plot could be Severus initially struggling to connect with Harry due to their past differences. But as he gets to know the extent of Harry's abuse, he becomes fiercely protective. He starts teaching Harry advanced magic privately, which helps Harry grow both in confidence and power.
The relationship may become more complicated. Severus might struggle with his own emotions. He might feel an urge to protect Harry from this fictional abuse, but at the same time, he has to deal with his long - standing animosity towards Harry. So, it could lead to a very strange and tense dynamic between them, with Severus trying to balance his new - found protectiveness and his old grudges.
Well, it's mainly because it gives a new perspective on the characters. Snape was always a complex character in the original series, and this scenario allows us to see a softer, more caring side of him. For Harry, it's a chance for him to get the love and care he was denied at the Dursleys.
One popular one could be 'Snape's New Beginning'. In this fic, Snape discovers Harry's abuse and takes him under his wing. It shows a different side of Snape, more nurturing than in the original series. Another might be 'Snape and the Abused Boy'. It delves deep into how Snape helps Harry overcome his trauma while also dealing with his own inner demons.
Severus is a very observant character. He may notice that Harry has a lack of certain basic skills or knowledge that a normal - cared - for child would have. For instance, Harry might not know how to handle simple social situations in a healthy way or might be overly defensive. This could lead Severus to suspect that Harry's home environment, where he should have learned these things, is not a healthy one and that he might be suffering abuse.