One possible plot could be Harry being influenced by dark magic artifacts. For example, he might find an ancient cursed object that gradually corrupts his mind and makes him turn dark. Another could be that he is betrayed by those he trusts, which pushes him over the edge into darkness.
Voldemort is often a key character. Since Harry is going dark, Voldemort might play a role in either guiding him into darkness or being an antagonist to his newfound dark power. Another common character is Hermione. She might try to save Harry from the dark path he's on, leading to a lot of conflict between them.
Well, in 'Harry Potter goes dark fanfiction', a common concept is the alteration of the wizarding world's power structure. Maybe Voldemort wins in a different way and Harry has to survive in a much harsher, more tyrannical regime. Or perhaps Harry himself becomes a sort of anti - hero, using the dark side of magic to fight against what he perceives as a greater evil, even if it means sacrificing some of his principles. And there could be the idea of dark magical creatures being used as weapons instead of just threats in the background.
Well, Sirius Black can be quite interesting in 'Harry Potter goes dark fanfiction'. If Harry goes dark, Sirius, who has always been a protector figure, might have to make some very difficult choices. He could either try to save Harry from the darkness or be forced to oppose him. Dumbledore is another character that stands out. His wisdom and manipulations would be under a new light in a dark fanfiction. And the Weasley family, especially Ron. His friendship with Harry would be severely tested if Harry goes dark, and his own character development could take some very different paths.
Well, a popular 'dark harry goes back in time fanfiction' is 'The Darkened Past Redone'. It's really interesting as it shows how Dark Harry's different perspective from his time - traveling affects the whole wizarding world's history. He makes some unexpected alliances and changes the course of many events. There are also stories like 'Time - Bent Dark Harry' which delves into his internal struggle between his dark self and the potential for change as he goes back in time.
Well, one possibility could be that Harry is driven by a deep sense of betrayal. Maybe he discovers some dark secrets about the wizarding world that make him question everything he has believed in. For example, if he finds out that Dumbledore has been using him all along for some self - serving purpose. This could push him towards the dark side as he feels that the so - called good side is just as corrupt.
Voldemort would surely be involved. He might initially be suspicious of Harry's sudden change but then see it as an opportunity to use Harry's power for his own dark ends. He could try to mentor Harry in the ways of dark magic.
Well, it could be about Sonic taking on a darker form or personality. Maybe there's some kind of evil influence that causes him to go dark, like a powerful dark artifact or an encounter with a really bad villain that messes with his mind and makes him turn against his friends.
Often, it starts with Harry having some sort of dark transformation or knowledge already. Then, when he goes back in time, he uses this to his advantage. For example, he might use his knowledge of future events to gain power or get revenge on those who wronged him.
Well, Harry could be really confused at first. Ouran is a very different world from Hogwarts. He might be shocked by the opulence of Ouran Academy and the strange club system there. Maybe he'd try to find a way to fit in while still being true to his wizard self.