Well, in this kind of fanfiction, this scene can have a huge impact. If it's written well, it can completely reshape their relationship. Harry might feel a sense of gratitude towards Snape, which is something he never thought he'd feel. Snape, on the other hand, might feel a strange sense of connection. It could be the start of a friendship or at least a more amicable coexistence. It also gives the writer a chance to explore the psychological aspects of both characters, like Snape's guilt and Harry's capacity for forgiveness.
There could be a fanfiction where Snape finds Harry unconscious with blood on him after a skirmish with some dark wizards. Snape's actions of washing the blood off are not just about cleaning but also a way to symbolize his internal struggle between his hatred for James Potter and his growing, albeit grudging, respect for Harry. This could lead to a complex character development arc for Snape in the story.
It can potentially start to thaw the icy relationship they had before. Just this simple act of physical contact might make Harry see Snape as less of an enemy.
The impact would be significant. Harry has always had a complicated relationship with Snape. When Snape discovers Harry is gay, it could shatter some of the pre - existing barriers between them. Snape, who has his own secrets and pain, might find a new connection with Harry. This could lead to a transformation in their relationship. Harry may start to trust Snape more, and Snape could finally let go of some of his old grudges against Harry. They could end up having a more positive and supportive relationship, which would be a huge change from their often - hostile past interactions.
The healing might make Harry feel indebted to Snape. This could change their relationship from one of animosity to one where Harry is more open to Snape. Snape, on the other hand, might still be his usual guarded self, but the act of healing could create a crack in the wall he has built between them. Harry might begin to question his previous assumptions about Snape and be more willing to cooperate with him in certain situations.
They would probably become like brothers. With Snape as their common father figure, they would have to learn to get along. Harry might be more forgiving of Draco's past actions, and Draco would have to let go of his animosity towards Harry.
It could make their relationship extremely hostile. Snape would likely be very angry at Harry for destroying something related to him, which would further strain their already tense relationship.
It could potentially improve their relationship. Snape might start to see Harry in a new light, which could lead to less hostility between them. Harry, on his part, might also gain a new respect for Snape if Snape acknowledges his potions skills.
He could be secretly worried. Snape might use his knowledge of potions and dark magic to try and find a cure or at least a way to stop the bleeding. He may also be conflicted, as his past relationship with Harry and his loyalty to different sides in the wizarding world play a role in how much he wants to help Harry.
It could be a dark magic curse. Maybe some enemy has cast a spell on Harry that is slowly sapping his health, leading to him coughing blood.
It would change it drastically. First, Snape would have to come to terms with this new relation. He might start seeing Harry not just as James Potter's son but as his own family. This could lead to him secretly mentoring Harry, guiding him in potions and in dealing with the darker aspects of the wizarding world. Their relationship could shift from animosity to a sort of guarded kinship, with Snape being gruff on the outside but having a newfound soft spot for Harry.