Another one is 'The Adoption of Harry by Snape'. It's a heartwarming story where Snape overcomes his prejudices. It focuses on how Snape's cold exterior melts as he gets to know Harry better. The author does a great job of showing how their relationship changes over time, from suspicion to mutual respect and finally a deep, familial love.
One popular 'Snape adopts Harry' fan fiction is 'A Father's Love'. It delves deep into how Snape, despite his initial reluctance, gradually grows to care for Harry like his own son. Another is 'Snape's New Family' which shows how Snape's adoption of Harry changes the dynamics within Hogwarts, with teachers and students alike reacting to this new situation.
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.
I'm not sure about a specific title, but generally in these types of fan fictions, the story often focuses on how Snape's adoption of Harry changes the course of Harry's life at Hogwarts. For example, Snape might use his knowledge of dark arts and potions to train Harry in a more private and intensive way. This could lead to Harry being better equipped to face Voldemort earlier. Also, the emotional aspect of their relationship, from Snape's initial reluctance to a growing father - like bond, is usually explored in great detail.
They're popular because it's an interesting 'what - if' scenario. Snape and Harry have a very complex relationship in the original books. So, seeing Snape take on the role of Harry's father flips their relationship on its head and allows for a lot of character development and new storylines.
One popular fan fiction could be 'Snape's New Family'. In this fic, Snape's decision to adopt Harry leads to a whole new dynamic at Hogwarts. Harry experiences a different kind of mentorship from Snape, which is far from their usual tense relationship in the original series. It delves deep into how Snape tries to protect Harry while also teaching him advanced magic.
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.
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.
The concept is popular because it's a fresh take on the relationship between Snape and Harry. In the original series, their relationship is complex and often antagonistic. This idea of Snape adopting Harry flips that on its head and allows for a more positive and nurturing relationship to develop.
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.
One big challenge is their pre - existing relationship. They've had a lot of conflicts in school. Snape has been rather harsh on Harry, so they need to overcome that animosity. Also, Snape has to deal with Harry's trauma from the Dursleys. He needs to help Harry heal and grow in a positive way, which is not easy for someone as emotionally reserved as Snape.