At the start, Fem Harry Potter would be in disbelief. She has her own life, her own goals, and suddenly she's being pushed into a marriage with Draco. As she realizes the situation is real, she could become very guarded. She might act coldly towards Draco, seeing him as part of the problem. But as she sees Draco's own discomfort with the situation, she could start to feel a bit of sympathy and the relationship could become more complex.
She would probably be furious at first. Harry is known for her strong will, and being forced into a marriage, especially with Draco, would go against everything she believes in. She might try to fight it directly, using her magic skills to break free from whatever is forcing this marriage.
Fem Harry Potter could initially feel completely betrayed. She might think that all her friends and the wizarding world she has known have turned against her. This could lead to her isolating herself. However, as she spends more time with Draco in this forced marriage, she could start to notice things about him that she never did before. Maybe she realizes that he has his own insecurities and that he's not just the spoiled bully she thought he was. This could gradually change her attitude towards him and the situation.
One way this plot could develop is through a political or family power play. In the wizarding world, marriages are sometimes used to strengthen alliances. Maybe the Malfoy family and some powerful wizarding families or political forces force the situation. Harry, being female in this fanfic, might initially resist but then gradually find some unexpected common ground with Draco as she gets to know him better in this forced situation.
One possible plot development could be that Harry tries to find a way to escape the marriage. She might use her magical skills and the help of her friends to break free from Voldemort's control. Another could be that she pretends to go along with the marriage while secretly planning to undermine Voldemort from within.
Luna would be very open - minded. She might see the fanfiction as just another form of magical thinking. She could find the wild and imaginative ideas in the fanfictions quite endearing and might even start to incorporate some of the concepts into her own unique view of the wizarding world.
Another possibility is that Lucius could be initially confused. He might not understand what he's seeing at first. After all, Harry and Draco are supposed to be enemies in the general wizarding world view. He could stand there for a moment, trying to process what's going on before taking any action.
Sirius may also be angry at first. Given his protective nature towards Harry, if he misinterprets the situation as Draco causing trouble for Harry, he would likely step in assertively. But if it's a situation where Harry and Draco have a more positive or friendly interaction in the fanfiction, Sirius would have to re - evaluate his initial reaction.
Naruko's friends would have a range of reactions. Her female friends might gather around her, giving her emotional support and advice. They would tell her to be strong and not let this forced marriage break her. The male friends, like Kiba, might be more ready to take action. They could try to intimidate those who are forcing the marriage. As for Sasuke's friends, they could be divided. Some might think this is a good opportunity for Sasuke to move on from his past and settle down. Others might worry that it will make Sasuke more withdrawn, as he might not be ready for such a commitment. They would all be watching the situation closely, ready to step in if things go wrong for either Naruko or Sasuke.
He might be shocked. Draco has always seen Harry as an equal rival in some ways, but finding out he is Lord Black means Harry has a whole new level of status. So, shock is a very likely initial reaction.
Well, Ron could get angry. He has a strong loyalty to Harry, and seeing Harry with Draco, who he has always seen as an enemy, might make him feel betrayed. He might immediately jump to conclusions and start shouting or demanding an explanation from Harry.
Kakashi would probably be a bit concerned. He cares about Naruto like a student and a son. He might talk to Naruto privately and tell him to give it a chance. At the same time, he could also have a word with Hinata's family if he feels the forcing is too much. As for Sakura, she might be a bit jealous at first, but then she would realize that Hinata is a good person and try to encourage Naruto to be more open - minded towards the marriage.
One reason could be some sort of ancient magical law or prophecy. Maybe there's a hidden clause that says for the greater good of the wizarding world, they need to be married. It could be related to some power or protection that their union might bring.