Draco may be motivated by a sense of justice. Even though he has his own past issues, he realizes that abuse is wrong and he can't stand by and let it happen to Hermione. It could also be that he wants to prove himself to be different from what everyone expects of him. By saving Hermione, he is showing that he is not the same Draco they thought he was.
One possible motivation could be that Draco has changed. He might have seen the error of his ways and decided to do the right thing. Another motivation could be that he has feelings for Hermione, even if they are not fully realized yet. He doesn't want to see her in a bad situation, so he steps in.
Well, it could completely shift the relationships in the story. Instead of Hermione being in a difficult situation with Ron, she now has an unexpected ally in Draco. This might lead to a new friendship or even a different kind of relationship between them. It could also make Ron realize his mistakes if he was indeed being abusive in the fanfiction.
Draco might be motivated by jealousy. He could be jealous of Ron and Hermione's friendship or a possible romantic relationship between them. So he tries to harm Hermione out of spite.
One possible scenario could be that Ron says something really mean to Hermione during an argument, and Draco, who has secretly been observing Hermione's intelligence and kindness, steps in to defend her. Maybe he uses his quick wit to shut Ron down verbally.
Draco could be seeking redemption. He may be tired of being on the wrong side of the war. Saving Hermione, who is a symbol of the good side, would be a significant step in his journey towards redemption. Additionally, he might be influenced by his friendship or alliance with some of the other characters who are on the side of the Order of the Phoenix. They could have convinced him to do the right thing and save Hermione from Bellatrix.
One motivation could be that Draco has developed feelings for Hermione. So, when he sees Viktor as a rival for her attention or a threat to her safety, he takes action to save her.
Well, in some versions, Ron might use his quick wit and knowledge of Hogwarts' secret passages to outmaneuver Draco. He could lead Hermione to safety through a passage that Draco doesn't know about.
One possible reason could be that Draco has had a change of heart. Maybe he realizes that Hermione is a person worthy of protection regardless of her House or her friendship with Ron. He might have seen some injustice about to befall her from Ron and his Gryffindor bravado getting out of hand.
Maybe Draco is jealous of Hermione's intelligence and abilities. In the fanfiction world, he could think that by making her his wife, he can somehow take credit for her achievements or keep her from outshining him. It could also be a power play. Draco might believe that having Hermione under his control through marriage would give him more influence in the wizarding world, especially if she has connections that he wants to use for his own gain.
Well, one plotline could be that Hermione is heartbroken by Ron's cheating. Draco, who has secretly admired her from afar, steps in to comfort her. This leads to them exploring a relationship that was previously unthinkable due to their houses' rivalry.
Over time, if the fanfiction progresses, Hermione could become a sort of bridge between Ron and Draco. She might encourage them to get along, now that Draco has shown that he can be on Hermione's side. Draco might also start to see Ron in a different way, realizing that Ron's jealousy or rudeness towards Hermione was born out of his own insecurities. This could potentially lead to a more complex and interesting dynamic between the three of them.