Snape would probably be very conflicted. On one hand, he has a long - standing grudge against James Potter, Harry's father. But on the other hand, he loved Harry's mother, Lily. So, he might be cold at first, but then his sense of protecting Lily's son could kick in. He would likely be very strict with Harry, as he is with all his students, but also secretly keep an eye on him to make sure he's safe.
Snape's reaction would depend on the circumstances of how he found Harry. If it was in a situation where Harry was clearly in danger from the dark side, Snape would feel a sense of obligation to protect him. He would be gruff and curt, but he would also use his skills to ensure Harry's safety. He might be hesitant to show any kindness openly, but in small ways, like making sure Harry has a warm place to stay or proper food, he would show his care. This discovery could also make Snape re - evaluate his relationship with Harry and the whole Potter family in general.
At first, Snape would be shocked and annoyed. He might think that Harry has gotten himself into another foolish situation. However, as he realizes the gravity of the situation, his true feelings for Lily would start to surface. He would try to hide his concern, but his actions would show that he's more worried about Harry than he lets on. For example, he might give Harry some special potions to help him recover if he's injured, all the while muttering under his breath about how much trouble Harry is.
Snape would likely be angry at first. Harry has always been a source of trouble in his eyes, and running away would just add to that perception. He might mutter some sarcastic remarks under his breath about Potter's irresponsibility.
He could also be secretly amused. Despite his stern exterior, Snape might see a bit of his own unrequited love in their relationship. So, he might give them a stern warning but not be as severe as he usually is.
Snape's reaction could also be one of extreme caution. He would be constantly on guard, worried that Harry might discover some of his secrets or that Voldemort's supporters might target Harry while he's in his care. So he would be very vigilant, but this might also lead to some over - the - top reactions when Harry does something even slightly out of the ordinary. However, over time, this vigilance could turn into a form of care as he gets used to Harry being around.
Snape would be deeply shocked and disgusted. Given his own experiences and the values he holds, finding Harry in a rape - related romance fanfiction would be like a blow to his perception of the world around Harry. He may initially be in disbelief, but then his anger would rise. He might try to find out who created such a disturbing fanfiction and perhaps try to put an end to it, as it goes against everything he believes in and the world he is a part of in the original Harry Potter series.
Harry would probably be quite resentful at first. He might think Snape is just being his usual unfair self. So, he would be sulky and do the tasks reluctantly.
He'd probably be annoyed. Snape is a serious wizard and he might think fanfiction is a silly Muggle - influenced concept.
Snape would likely be initially suspicious. He's not used to Harry coming to him for help or sharing secrets. But once he realizes the seriousness of what Harry is saying, he might start to see Harry in a new light. He could be grudgingly helpful, still maintaining his cold exterior but secretly starting to feel a bit more protective of Harry.
Snape might also keep what he saw to himself at first. Instead of immediately confronting them, he could choose to observe them further. He might be curious about what they were really up to and use his skills as a spy to find out more. This way, he could gather more information before deciding on the best course of action, whether it be punishment or something else entirely.
Harry would probably be very confused at first. He's so used to Snape's animosity towards him that when Snape forgets who he is, it would be a complete shock. He might also be a bit suspicious, thinking it's some sort of trick. But as time goes on, he could start to feel a bit of pity for Snape, especially if Snape seems lost or confused without his memories of Harry.
The Slytherin house would probably be outraged. Snape is one of their own, in a sense. They would demand justice for Snape and might even use this incident to fuel their long - standing rivalry with Gryffindor. There would be a lot of tension and conflict within the Hogwarts community as a result of this act.