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.
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.
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 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.
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.
Yes, there are some fanfictions with this concept. It's an interesting take on the Harry Potter universe as it flips the typical relationship between Harry and Voldemort. In these fanfictions, the story often explores how Voldemort's actions change when he takes on the role of an adoptive figure to Harry, who has been abused. It can lead to some really unique character developments and plot twists.
One great fanfiction in this genre is 'A New Beginning' where McGonagall steps in to rescue Harry from his abusive relatives. It beautifully shows how she nurtures him and helps him grow in confidence.
His personality also becomes more open. He has to communicate with Harry in a more honest and open way. He can't keep all his thoughts and feelings bottled up like he used to. He has to share his wisdom and experiences with Harry, which in turn makes him more approachable and less of the brooding, closed - off person he was before in the official story.
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.