Magic within him could play a role. The love magic that protected him as a baby might still have some lingering effect. Also, his connection to his friends and their unwavering belief in him could give him the strength to hold on. For example, if his friends are out there searching for him and he can sense their determination, it can keep him alive during the torture.
He survives through his strong willpower. Harry has always been a determined character, and that could help him endure the torture.
Harry might cope by retreating into his own thoughts and memories of his parents and the wizarding world. For example, he could think about the good times at Hogwarts to endure Vernon's torture.
He could survive through his strong will and Occlumency skills. By blocking Voldemort from fully penetrating his mind, he can keep his most important secrets safe and hold on to his sanity, which is crucial for survival.
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.
Harry might maintain his sanity through his memories of Hogwarts. The thought of his friends, the magic he has learned, and the happy times at school could be his mental refuge. For example, he could recall the fun times in Potions class or flying on his broomstick during Quidditch matches.
It could start with a lot of animosity on Harry's part, but as he is trained, he might start to see Voldemort in a different light. Maybe he begins to understand Voldemort's motives, though not necessarily agreeing with them.
Well, it might make him more cynical at first. After all, he has just absorbed the essence of the most evil wizard. But then he could use this newfound darkness within him to better understand the bad in the wizarding world and fight it more effectively.
Well, he might use his knowledge of magic in unexpected ways. For example, he could use a simple spell in a complex situation that Voldemort wouldn't anticipate. Harry has always been good at thinking on his feet.
Harry in this fanfiction is likely to be more ruthless. Voldemort's upbringing would make him less empathetic. He may value power above all else and be more willing to use dark magic to achieve his goals. His relationships would also be different. He wouldn't have the same close - knit group of friends as in the original story. Instead, he might be surrounded by Death Eaters or those who follow Voldemort's ideology.
Harry could also try to reason with Voldemort. He might remind Voldemort of the prophecies and how killing him might not be in Voldemort's best interest. He could also try to appeal to any bit of humanity that might still be left in Voldemort, although that's a long shot.
It changes the canon by introducing a new form of interaction between Voldemort and Harry. Instead of just the typical battles and mind - reading attempts we see in the original books, the 'plugging' concept adds a more invasive and direct connection. For example, Voldemort could directly influence Harry's thoughts and actions in ways that were not possible in the canon.