Well, Harry is a brave character. So, he would probably be full of anger and disbelief. He might start yelling at Snape, demanding an explanation for such an inappropriate act. He would also be thinking about how to escape and report this to his friends or the proper authorities in the wizarding world, like Dumbledore.
One possible reason could be punishment. Snape has always had a rather thorny relationship with Harry in the original series. He might see this as a way to assert his authority over Harry. Maybe Harry has done something in the context of the fanfiction, like accidentally messing up Snape's potion ingredients or getting into an area of Snape's house where he wasn't supposed to be.
Fanfiction often has a wide range of themes and interpretations. Instead of focusing on inappropriate or adult - themed concepts, you could look for fanfiction that focuses on the friendship or mentorship between Harry and Snape. For example, stories about how Snape secretly helps Harry improve his Potions skills in a more appropriate and platonic way.
He probably feels angry at first. Harry has always been a bit of a rebel, and being forced to do such a task by Snape, who he doesn't particularly like, would surely make him fume. He might feel it's unfair, especially if he hasn't really done anything wrong.
Well, Harry could react with a great deal of suspicion. Since he and Snape have had a rocky relationship, he might think Snape is up to no good. He could try to gather his friends, like Ron and Hermione, to help him figure out what Snape's real motives are. Harry might also try to use his own wits and magic skills to outsmart Snape if he feels that Snape is being unfair or dangerous in his forcing of actions. He could also be very conflicted, on one hand wanting to trust Snape as Dumbledore did, but on the other hand being very wary due to their past interactions.
There should be family - friendly Harry Potter fanfiction that doesn't involve inappropriate words like those. The official Harry Potter world has a large amount of positive, creative fan - made content that focuses on the magic, friendship, and adventure aspects of the story, rather than using offensive language.
One alternative could be fanfiction that focuses on Snape mentoring Harry. For example, Snape could be teaching Harry advanced potions techniques or helping him understand the history of dark magic in a way that Dumbledore couldn't. This would show a more positive and educational relationship between them.
Well, Snape might use his knowledge of both boys' strengths and weaknesses. For Harry, he'd understand his Gryffindor courage but also his impulsive nature. With Draco, he'd be aware of his Slytherin pride and family influence. Snape could set similar rules for them in terms of magic study and behavior, while also respecting their individual personalities. He might encourage Harry to be more cautious and Draco to be more empathetic.
One plot could be that Snape, under some dark magic influence, forces Harry to accompany him on a dangerous mission to retrieve a lost magical artifact. Snape believes Harry has some hidden power that can help. Another could be Snape forcing Harry to study a very advanced and dangerous form of magic, thinking it will protect Harry in the long run. And there could also be a plot where Snape forces Harry to enter a magically sealed area to face some long - forgotten threat that only Harry can potentially defeat.