It could change in a more positive way. In detention, they might have to rely on each other to get through Snape's tasks. If they are made to work on a complex magical experiment, they would need to communicate. This communication could break down some of the barriers between them. Maybe they start to exchange a few friendly words outside of detention, slowly building a more amicable relationship.
Well, perhaps Snape sets them to clean the potions classroom. Draco tries to boss Harry around at first, but Harry refuses to be pushed. As they clean, they accidentally knock over a vial that releases a magical mist. The mist makes them relive some of their worst memories involving each other. This forces them to understand each other's perspectives better and by the end of detention, there's a less hostile air between them.
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.
Their relationship can develop as they are forced to spend time together during detention. Harry might start to see Snape's tough exterior as a mask for his insecurities or past traumas. For example, when Snape shares a bit of his knowledge about a difficult potion, Harry realizes Snape is not just out to get him.
In fanfiction, when Snape and Hermione are in detention, their relationship could transform in several ways. Snape may be used to seeing Hermione as just another Gryffindor student who challenges his authority. But in detention, if she shows an aptitude for something he values, like a deep understanding of a particular potion or a magical theory. He could start to view her as an equal in some ways. Hermione, who has always seen Snape as a mean teacher, might find out that he has his own reasons for his behavior. Maybe he was bullied as a student too. This new knowledge could soften her view of him, and they could develop a relationship based on new - found respect and a bit of empathy.
The relationship would be drastically different. Harry, who has always seen Snape as a rather unlikable figure, would start to see him in a new light. He might come to respect Snape as a father figure. Draco, who has some connection to Snape through his family, would now have a more personal and perhaps more positive relationship with Snape. Snape himself would have to soften his usual harsh demeanor towards Harry. And between Harry and Draco, they would be forced to get along better as they are now under the same roof. They might start to understand each other's insecurities and backgrounds more.
In a Harry and Snape detention fanfiction, Harry might finally have a chance to understand Snape better. He could see that Snape's strictness is not just pure malice but perhaps a result of his complex past. Snape, on the other hand, could start to see Harry not just as James Potter's son, but as an individual with his own struggles. They might end up having a conversation about magic that neither expected, leading to a newfound respect for each other.
In the fanfiction, Snape's impression might make him more protective of Harry. He could start to subtly look out for Harry's well - being, whether it's in the face of other students' bullying or more dangerous threats from the dark side. This would be a significant change from their usually strained relationship in the original story.
Well, Harry could be forced to clean the Potions classroom during detention. Snape might make him scrub every cauldron by hand while muttering about how clumsy Gryffindors are. Harry might accidentally spill a potion ingredient, which makes Snape even angrier and gives him more tasks to do, like sorting out all the potion ingredients in the store cupboard.
It often changes for the better. After Harry apologizes, Draco might be initially skeptical. But as they start to interact more, they could become friends or at least develop a mutual respect. For instance, they might start sharing their experiences during the war, which helps them understand each other better.
To make a Harry and Snape detention fanfiction interesting, you can focus on their character development. For example, show Snape's internal struggle between his dislike for Harry based on his past with James and his duty as a teacher. For Harry, explore his growing understanding of the adult world and how Snape fits into it. Also, add some mystery elements like a hidden potion ingredient that they discover during the detention.