Harry would be completely shocked. He's known Hermione as his best friend and to see her with Lucius, who was once a Death Eater, would be almost unthinkable. He'd probably try to convince Hermione that she's made a huge mistake.
The Weasley family would be very concerned. Mrs. Weasley would probably be the first to voice her objections, thinking that Lucius is bad news. Ginny would be confused as well, having been friends with Hermione. She might try to get Hermione to open up about how this relationship came to be, while also being worried about what it means for the wizarding community at large.
Ron would be outraged. He's always had a bit of a protective streak when it comes to Hermione. He might even think that Lucius has somehow bewitched Hermione and would try to break them up by any means necessary, like challenging Lucius to a wizard's duel.
The other Hogwarts professors would be very concerned. McGonagall would likely be the first to take action. She would try to use the proper channels within the wizarding world to free Hermione. Snape, on the other hand, might have a more complex reaction. Depending on his own allegiances at the time in the fanfiction, he might be secretly helping or hindering the situation.
The reactions would be diverse. In the Harry Potter universe, Ginny Weasley might be a bit jealous at first, seeing Hermione having such an amazing father figure. Neville Longbottom would probably look up to Hermione even more, seeing her as having an even greater heritage. In the Marvel world, Natasha Romanoff would be interested in how Hermione's upbringing in the wizarding world has shaped her, compared to Steve's upbringing in the military. Clint Barton might be a bit indifferent at first but would soon realize the significance of this connection. And the new generation of superheroes in the Marvel universe would see Hermione as a bridge between their world and the magical world, and would be eager to learn from her.
The Death Eaters would probably be divided. Some might see it as a great opportunity to gain more power through this union, while others might be suspicious of Hermione and worry that she will be a threat to their cause. The students at Hogwarts would be in an uproar. Hermione's friends would be ready to fight for her freedom. Ginny, for example, would be a strong advocate for Hermione. And Neville, who has grown so much in courage, would also stand up against this wrong - doing. There would be a lot of tension and drama within the wizarding community as a whole.
Bakugo Katsuki, on the other hand, might be more dismissive at first. He'd think it's all just some made - up nonsense that has nothing to do with real hero work. But if he found a fanfiction that had an interesting battle scenario or a strong - willed character, he might grudgingly admit it had some merit. He'd probably scoff at any overly emotional or sappy parts though.
Harry could be initially shocked but then very happy for them. He might see it as a sign of hope in the midst of all the darkness. Ginny, on the other hand, could be a bit jealous at first, but then come to accept it and even give Hermione some relationship advice.
Harry would probably be extremely shocked. He has a deep respect for both Hermione and Severus in different ways, and this situation would completely turn his world upside down. He might initially be angry or confused, but then try to understand what led to this. Ron, on the other hand, would likely be more openly outraged. He has always had a bit of a jealous streak when it comes to Hermione, and this would be a very difficult situation for him to accept.
Harry would likely be very protective of Hermione. He's her best friend, after all. He might confront Draco immediately and try to get Hermione to see that she doesn't deserve this. Ron would probably be angry too, and might even be more impulsive in his reaction, perhaps getting into a fight with Draco.
Sakura would probably be shocked. She knew the Akatsuki was powerful, and Naruto killing them all might make her see Naruto in a whole new light, perhaps as a more dangerous or powerful figure than she initially thought. Kakashi, on the other hand, might be worried about the implications. He would be proud of Naruto's strength but also concerned about the power vacuum and how it could affect the balance of the ninja world.
Hermione's character might develop a new sense of understanding towards those on the 'dark side'. Through her time - traveling experiences with Lucius, she could see that not all who seem bad are completely irredeemable. She may become more open - minded and less quick to judge based on a person's family or initial appearance.
Harry would be really shocked. He's used to seeing Hermione as his friend and fellow Gryffindor. If she was suddenly Draco's sister, he'd be very suspicious at first. He might think it was some kind of Slytherin plot. Ron would be even more flabbergasted. He has his own issues with Draco and to think that Hermione was related to him would be hard for Ron to accept. He might even be a bit jealous that Hermione now has this connection to a pure - blood family.