It could also be that Snape finally decides to let go of his grudges. He understands that Harry is just a child caught up in a big, dangerous game. He wants to make amends for his past harsh behavior towards Harry and starts to be nice as a way of atoning for his actions.
Maybe Snape starts to see Lily, Harry's mother, in Harry. Since he loved Lily deeply, this resemblance makes him want to protect and be nice to Harry. In fanfiction, this emotional connection can be explored in more depth, like Snape having flashbacks of Lily when he looks at Harry.
One reason could be that he realizes Harry has a lot of potential and wants to nurture it. He sees that Harry is in a difficult position, being the target of Voldemort, and decides to help him despite their past differences.
One reason could be to add a shock factor. It completely changes the expected family relations in the original story. Another reason might be to explore Snape's character more deeply. If Harry is his son, it gives a new perspective on Snape's actions and emotions towards Harry throughout the series.
One possible reason could be that fanfiction often takes creative liberties that may distort the complex character of Snape that J.K. Rowling created. Snape has a very intricate backstory and personality in the original series, and fanfiction might simplify or misinterpret it.
In some fanfictions, Snape might share some of his knowledge about the wizarding world's secrets with Harry. Maybe he tells Harry about certain spells or magical artifacts that could help Harry in his fight against Voldemort. This act of sharing knowledge is a way of being nice as it gives Harry an advantage in his battles.
Isolation. Snape is a lonely character. He doesn't have many friends, and he is constantly in a difficult position between the Death Eaters and the Order of the Phoenix. His feeling of being alone and not being fully understood by anyone can lead to crying in fanfiction.
One possible plotline could be that Harry breaks a major Hogwarts rule, like sneaking into the Forbidden Forest. Snape catches him and decides that a severe punishment is in order, which in this case is spanking. Another could be that Harry fails a very important Potions test repeatedly, and Snape, frustrated with his lack of progress, resorts to this extreme form of discipline. However, these are all just fan - created ideas and not part of the official story.
One reason could be redemption. Harry realizes that Snape has had a very difficult life and has been on the right side all along, despite his harsh exterior. Harry, being the kind - hearted person he is, would want to save Snape to give him a chance at a better life after all the sacrifices he has made for the wizarding world. For example, Snape's love for Harry's mother Lily was so strong that he dedicated his life to protecting Harry, so Harry might feel a sense of indebtedness.
One possible reason could be the extreme stress he endures. In many fanfictions, Snape has to constantly balance his double - agent role during the war. The pressure of keeping his true loyalties hidden from Voldemort and his Death Eaters while also trying to protect the students at Hogwarts can be overwhelming, leading to a collapse.
One possible role is that the ring serves as a key to a hidden magic. Maybe it unlocks a secret chamber or a powerful spell that only Snape, with his knowledge, can figure out how to use for Harry's benefit.
Perhaps in this fanfiction, Snape shows a side of himself that is completely different from what Harry has known. He might be more open and honest with Harry, sharing secrets that make Harry believe he can be trusted. Like Snape might disclose some long - held information about Harry's parents that only he knew, which makes Harry think Snape has been on his side all along.
One reason could be guilt. In the original story, Snape had some complex feelings towards Harry's father. By protecting Harry in fanfiction, he might be trying to make up for the past. It's like he's trying to right the wrongs that were done to Harry间接 because of his relationship with James Potter.