One idea could be that Snape takes Harry in secretly. He teaches Harry advanced potions and magic in a more personal way, away from the prying eyes of Hogwarts. Harry begins to see Snape in a new light, not as the mean professor but as a strict yet caring guardian.
One interesting plot could be that Snape, in raising Harry, discovers a new side of the boy. He realizes that Harry has a natural talent for potions that was overlooked. Snape starts to teach Harry advanced potions techniques, and they form a sort of begrudging respect for each other. Harry begins to understand Snape's past and why he was so bitter, which changes their relationship for the better.
Well, it would completely turn the story on its head. In the original, Snape is an adult figure and often at odds with Harry. But if Harry were to raise Snape, perhaps Snape would grow up with a different view of Harry. He might not be so bitter and resentful. Harry could instill in him values that would make Snape less likely to be drawn to the Dark Arts. This would also mean that the whole Hogwarts dynamic would change. Snape might be a much more positive influence on the students instead of the intimidating figure he was in the original story.
Well, it changes their relationship a great deal. Usually, in the original story, Snape and Harry have a very antagonistic relationship. But in fanfictions where Snape raises Harry, they start to understand each other better. Snape sees Harry as more than just James Potter's son, and Harry realizes that Snape has his own reasons for his actions.
If Snape raised Harry, Harry would likely become a much more skilled potions master at an earlier age. Snape's knowledge and strict teaching methods would push Harry to excel in that area.
The story could also impact the fight against Voldemort. Hermione's knowledge and skills, enhanced by Snape, could give the Order of the Phoenix an edge. She might be able to develop new spells or strategies to combat the Death Eaters. Also, her relationship with Snape could lead to some unexpected alliances within the wizarding world, as people might be forced to re - evaluate their opinions of both of them.
Well, I know a fanfiction titled 'Blind Harry's New Guardian'. In this story, Snape is forced to take care of Harry due to certain circumstances. It's interesting to see how Snape deals with Harry's blindness, from teaching him magic in a different way to protecting him from the dark forces that still lurk. There's also 'Snape's Charge: Blind Harry' which has a unique take on their relationship, with Snape having to balance his past grudges and his newfound responsibility.
One possible fanfiction could be about Snape taking Hermione under his wing after realizing her extraordinary intelligence and potential. He might secretly tutor her in advanced potions and dark arts defense, leading to a unique bond between them. This could also cause some conflict with other Hogwarts staff and students, as Snape has a rather infamous reputation.
Snape becomes more empathetic. He has always been a complex character, but in this scenario, he has to open up his heart to Harry. His cold exterior starts to crack as he sees Harry's vulnerability. For example, he might show small acts of kindness like making sure Harry has enough to eat or a warm place to sleep.
The concept is interesting because it flips the traditional relationship between Snape and Harry. Snape, who was often at odds with Harry in the original story, now has to be his caregiver. It creates a whole new dynamic. Also, Harry's blindness adds an extra layer of vulnerability, and seeing how Snape reacts to that, whether with his usual gruffness or hidden tenderness, is fascinating.