I'm not sure if there is a specific fanfiction with that exact plot. Fanfiction is a vast world, and while there might be some out there that explore unique and unexpected scenarios between Harry and Snape, this one seems rather unusual. You could try searching on popular fanfiction websites like Archive of Our Own or Fanfiction.net.
Harry could be following a hunch. He might have found some evidence that links Snape to a solution he needs. For example, he could have discovered a note written by his father or mother that mentions Snape's ability to deal with a certain type of dark magic that is now threatening Harry. So, he takes a chance and goes to Snape, hoping against hope that Snape will be willing to help.
In this kind of fanfiction scenario, Snape might initially be conflicted. On one hand, he has his long - standing dislike for James Potter, Harry's father. But on the other, his sense of duty as a Hogwarts professor could kick in. He might reluctantly start to heal Harry, all the while muttering under his breath about how much trouble Harry always seems to get into, just like his father. Then, as he heals Harry, he might start to see some of Lily, Harry's mother, in him and soften a bit.
In some fanfictions, Snape is indeed portrayed as Harry Potter's father. Fanfiction allows for creative reinterpretations of the original story, and this is one such interesting deviation from the canon where Snape's complex relationship with Harry takes on a whole new dimension.
Perhaps in this fanfiction, Snape has proven himself to Harry in some extraordinary way. Maybe he has saved Harry's life multiple times or has shown his true loyalties that were hidden in the original story. It could also be that Snape has some special connection with Harry that makes Harry trust him unconditionally.
In the fanfiction, Snape could be in a really tough situation when Harry comes to him for help. On one hand, he has his loyalty to the Dark Lord (or at least that's what others think), and on the other, there's this boy who is the son of the woman he loved. He might end up guiding Harry in a very roundabout way, like giving him a potion ingredient that has a hidden meaning or leading him to a certain book in the library that contains the solution to Harry's problem.
Well, it might seem a bit odd at first. Snape has such a complex relationship with Harry in the original story. But on the other hand, fanfiction can offer different perspectives on the characters. Maybe he likes it because it shows different interpretations of the wizarding world he's a part of.
Well, it depends on the specific fanfiction. Different authors have their own interpretations and creative directions, so Harry Potter may or may not be as Snape thinks.
It would be a very strange and unique piece of fanfiction. Given the nature of the relationship between Harry and Snape in the original series, which is often tense and full of animosity, this scenario would completely flip the dynamic on its head. It would likely be a very character - driven piece, exploring new facets of their personalities.
One possible plot could be that Hogwarts is facing a new and powerful dark magic threat. Maybe a long - lost dark wizard's spell has been activated and is slowly draining the magic from the school. The students and teachers then have to work together to find a way to reverse the spell. They might search through old tomes in the restricted section of the library and go on adventures outside the school to gather rare ingredients for a counter - spell.