Maybe Draco discovers a hidden weakness of Voldemort. Draco, having been raised in a pure - blood family, might have access to some ancient magic knowledge. He uses this knowledge to create a situation where Voldemort is temporarily incapacitated, giving Harry the chance to escape or defeat Voldemort. For example, he could find a way to disrupt Voldemort's connection to his Horcruxes for a short time.
Another possibility is that Draco has a change of heart towards Harry. He realizes that Voldemort's ideology is wrong. So, when Voldemort is about to attack Harry, Draco steps in and uses his own magic to shield Harry. This could be a moment of great sacrifice on Draco's part, as he would be defying Voldemort directly, which is extremely dangerous considering Voldemort's power and cruelty.
One motivation could be self - preservation. Draco might realize that if Voldemort kills Harry, it will lead to an all - out war that could destroy everything he knows. By saving Harry, he hopes to find a more peaceful solution and protect his own family and the wizarding world in a broader sense.
Well, it could be that Draco has a change of heart early on. He realizes that the Dursleys are truly awful to Harry. So he uses magic to create distractions. He could make strange things happen around the house that scare the Dursleys so much that they just want Harry to leave. Then Draco could be waiting outside and whisk Harry away to a safer place, like a hidden place in the wizarding world where he has set up a little haven for Harry.
Well, perhaps Harry uses his quick thinking and his knowledge of magical creatures. He might step in just in time, using a spell to distract Buckbeak before it can harm Draco. For example, he could use a simple levitation spell to lift a small object and draw Buckbeak's attention away from Draco.
In this fanfiction, Harry might also save Draco by appealing to Lucius' sense of self - preservation or family. He could threaten to expose some of Lucius' secrets or illegal activities if he doesn't let Draco go. Or, if there is some underlying family drama involved, Harry could use that to his advantage. For instance, if there's a feud within the Malfoy family that Harry is aware of, he could manipulate the situation in a way that makes Lucius back off and leave Draco unharmed.
In this fanfiction, it could be that Voldemort has a premonition. He sees that if Harry Potter dies, it will lead to a series of disasters that will also destroy his own plans. So, in order to preserve the balance or to keep his long - term goals intact, he saves Harry. For example, if Harry's death causes an uncontrollable chaos in the wizarding world, Voldemort's rule over the dark forces might be disrupted. So he steps in to save Harry.
Love. In fanfictions, it's a common motivation. Draco might have fallen in love with Hermione over time, and that love drives him to risk his life to save her from Voldemort.
In some fan fictions, Voldemort might save Harry from the Dursleys out of a newfound sense of self - interest. Maybe he realizes that Harry has some power or knowledge that he needs, and by rescuing him from the Dursleys, he can gain Harry's trust and access that. For example, if there is a prophecy that only Harry can unlock and Voldemort believes it will help him achieve ultimate power, he would take Harry away from the Dursleys who are mistreating him.
Well, it could be that Harry discovers Draco's plan in advance. He then sets up a counter - plan. When Draco tries to harm Ginny, Harry jumps in, using his invisibility cloak to his advantage, surprising Draco and rescuing Ginny.
Well, it could start with Draco being forced into this 'pet' - like situation by Voldemort. Maybe at first Draco is terrified, but as time goes on, he might start to understand Voldemort's motives a bit more, and their relationship could become more complex, with Draco having to do Voldemort's bidding while also trying to find a way out.
In this fanfiction, Harry joining Voldemort could be a catalyst for Draco to re - evaluate his own beliefs. As they are both in Voldemort's orbit, they are forced to rely on each other. Draco might find himself protecting Harry from the more extreme Death Eaters, and through these shared experiences, their relationship could grow from animosity to something more complex and perhaps even romantic.