Draco might immediately become defensive. He would probably try to shield Hermione from his father's wrath at first. He could also be filled with fear, knowing how strict and unforgiving his father can be.
Another reaction could be that Draco stands his ground and defies his father for once. If his feelings for Hermione are strong enough, he might not be willing to let Lucius come between them. This could be a turning point in his character development in the fanfiction, showing that he's growing out of his father's shadow and becoming his own person.
Hermione might initially be shocked and afraid, but she would quickly gather her wits. She would assess Draco, trying to figure out if there was any way to sway him to her side. Given her ability to see the good in people, she might try to appeal to any sense of morality Draco has left, all while secretly planning her escape or a way to undermine Voldemort's plan of using her as a pawn against the good side.
Hermione might be shocked at first. She has always seen Draco as an adversary, so a neck kiss from him would be completely unexpected. She could push him away immediately and demand an explanation.
She would most likely be furious. Hermione is a smart and independent character. She would immediately start planning her escape. She might use her knowledge of magic to try and outwit Draco.
Draco's relationship with Hermione could change drastically. He might start to feel sympathy for her, which could turn into a reluctant friendship. Lucius, however, would be more resistant to any positive change. But as Hermione shows her strength even while injured, he might develop a begrudging respect. Overall, Draco could become more of an ally to Hermione, while Lucius would be in a more complex situation of having to re - evaluate his views due to Draco's new attitude.
Another reaction could be confusion. Draco might not know how to feel. On one hand, he has his Slytherin pride and his clothes are part of that. But on the other hand, seeing Hermione in his clothes gives him a strange feeling in his stomach. He might end up being more curious about Hermione and her reasons for wearing his clothes.
Hermione could also be very hurt. Her hair is part of her identity, and having Draco, who she already has a strained relationship with, do something so cruel would cut deep. She might go to her friends, Harry and Ron, for support. They would likely be just as angry as she is and plot some sort of revenge against Draco and his Slytherin friends.
Hermione's friends from Gryffindor would be a mix of disbelief and concern. Neville, for example, would be worried that Draco might be using Hermione in some way. Luna would be more accepting, seeing it as a unique and interesting relationship that defies the norms of the wizarding world. As for Draco's friends from Slytherin, they would also be shocked. Some might see it as a betrayal of Slytherin values, while others might be intrigued by the power dynamics at play between a Muggle - born witch and a pure - blood wizard.
Hermione's parents might be initially shocked. They know Draco's family's history and reputation. But if they see how much Hermione loves him and how Draco has changed, they could come around. They would likely be more concerned about Hermione's happiness in the long run.
Harry and Ron would probably be shocked at first. Ron, especially, might have a hard time accepting it because of his past relationship with Hermione. But eventually, they would come around because they care about Hermione. Ginny would likely be more open - minded and try to be supportive. Other friends from Hogwarts might also be divided, some might be against it because of the long - standing rivalry between the Gryffindors and Slytherins, while others would see it as a chance for unity in the wizarding world.
He might be very embarrassed. Howlers are known for delivering their messages in a rather loud and public way. Draco, who is used to maintaining an image of superiority, would find it humiliating to have his family's business aired out in front of his classmates.