One possible reason could be Dumbledore's manipulation. Dumbledore might see it as a way to keep Harry safe under Severus' watchful eye, knowing Severus' skills in magic and his loyalty (in his own complex way). Another reason could be a magical binding or an old wizarding law that, due to certain circumstances, forces Severus into this situation. For example, if Harry's magical protection is somehow linked to Severus in a way that adoption is the only solution to maintain that protection.
At first, Severus would likely be extremely resistant. His cold and often bitter personality would be on full display. He might be very strict with Harry, not out of malice but because he doesn't know how else to handle the situation. However, over time, he would gradually soften. His protective instincts, which are there deep down, would start to surface. For example, he might start to show concern for Harry's well - being in small ways, like making sure he has proper potions for any ailments.
Harry might develop from being resistant to the marriage to being more open - minded. He realizes that Severus is not just the strict teacher he once thought. For Severus, he may start to soften his tough exterior. He begins to see Harry not as James Potter's son but as an individual with his own merits.
At first, their relationship would be full of hostility. Harry would be angry about being forced into this marriage with Severus, who he has had a complex history with. Severus, on the other hand, might be indifferent or even disdainful.
One popular 'the marauders adopt severus fanfic' is 'The Marauders' Newest Member'. It's really interesting as it shows how the marauders gradually accept Severus into their group and how Severus adapts to this new situation.
In many Severus and Harry fanfics, their relationship is often re - imagined. Sometimes it's a mentor - mentee relationship that goes deeper than in the original books. For example, some fics might explore how Severus, with his complex past and knowledge, can help Harry grow not just as a wizard but also as a person, despite their initial animosity.
Well, 'Under the Cloak of Night' is a Severus and Harry fanfic that stands out. In this story, it presents a more nuanced view of their relationship outside of the regular Hogwarts setting. There's also 'The Unlikely Pairing' which is quite interesting. It takes the idea of their potential friendship and runs with it, showing how they can overcome their differences. Additionally, 'In the Shadows of the Castle' gives a unique take on their bond, with a lot of character development for both Severus and Harry.
In some fanfictions, the forced marriage could lead to a situation where Harry and Severus have to protect each other from external threats. Harry's status as 'The Boy Who Lived' makes him a target, and Severus's past associations also put him in danger. As they face these threats together, they start to rely on each other. This mutual reliance then turns into a deeper emotional connection.
One possible plot development could be that at first Harry is extremely resistant. He might try to find ways to break the forced marriage. Maybe he'll seek help from his friends like Hermione and Ron. They could try to look for magical laws or loopholes to dissolve the situation.