Talking to Sirius Black was crucial. Sirius told Harry about his parents' time at Hogwarts, their friendship group, and the secrets of their Order of the Phoenix days. Sirius was like a window into Harry's parents' past.
The Pensieve was also a source. Harry was able to see his father's memories in Snape's Pensieve. This showed him a different side of his father and how his parents' generation dealt with the threat of Voldemort at school.
He learned a great deal from Hagrid. Hagrid was the one who first told Harry about his parents' death and how they were killed by Voldemort. Hagrid also gave Harry the photo album which showed pictures of his parents and their friends.
In some fanfictions, Harry might use extremely powerful and ancient magic. Maybe he discovers a long - lost spell during his adventures that has the power to reverse death. For example, he could find a spell hidden in a forgotten corner of the Hogwarts library that was created by a powerful wizard in the past but was deemed too dangerous to be used.
One possible reason could be that he might feel abandoned. Growing up without them, he could resent the fact that they left him an orphan. He might think that if they were really so great, they would have found a way to survive and be there for him.
In theory, it is possible in fanfiction. One way could be through time - travel magic. Harry could discover a powerful time - turning spell that allows him to go back in time to the moment before his parents' deaths. He would then use his skills and knowledge from his own time to fight off Voldemort and save them. For example, he might use advanced defensive spells he learned at Hogwarts to counter Voldemort's attacks.
Yes, there might be some extremely dark and out - of - canon fanfictions out there with such a disturbing premise, but it goes against the general nature of the original story where Harry's parents loved him deeply. However, in the vast world of fanfiction, people can create all kinds of strange and often inappropriate scenarios.
On a more magical level, reviving the dead is against the natural order of things in the wizarding world. This could attract unwanted attention from magical authorities or even dark forces. Some might see Harry's act as a dangerous precedent and try to either stop him or use his new - found power for their own evil purposes.
Well, in some fanfictions, Harry might draw on his own experiences facing dark magic. He could use his adventures with Voldemort as real - life examples to make the lessons more vivid. For instance, when teaching about defensive spells against the Imperius Curse, he could talk about how he resisted it in his encounters.
They might be shocked. After all, Harry's past is full of adventures, danger, and mystery. They could be in awe of their father's courage in facing Voldemort from such a young age.
The plot would change drastically. Harry would not be living with the Dursleys, so there would be no need for him to escape that horrible situation. Voldemort might have a harder time targeting him as his parents would be on high alert. There would be no letter - hunting drama. Also, his relationship with Snape would be different as his father was Snape's rival. His parents could have taught him some advanced magic from a young age, which would make him stand out at Hogwarts in a different way than in the original story.
Well, in fanfiction, it might be that a magical object has the power to bring the dead back to life. For example, a long - lost and extremely powerful enchanted amulet. When Harry discovers this amulet, it has the ability to restore his parents to life. It could also be that a benevolent and extremely powerful being decides to intervene and resurrect the Potters for the sake of Harry and the greater good of the wizarding world.
Perhaps his parents were part of a secret and evil organization all along. They pretended to be good but in fact were planning something big and Harry was just a pawn in their plan. So they betrayed him by leaving him exposed to danger or even trying to harm him directly. In the fanfiction, Harry could then go on a journey to discover the truth about his parents and their real motives.