One possible plot could be that Harry is transported to the world of the Fellowship through some sort of magical portal. Once there, he realizes that the dark forces they are fighting are related to the dark wizards in his own world. So he decides to join them wholeheartedly. He then uses his Gryffindor courage and magical abilities to assist in their journey. He might help Aragorn in his claim to the throne by using magic to prove his rightfulness, or he could use magic to communicate with Gandalf in a more efficient way during their travels.
In this fanfiction, perhaps Harry joins the Fellowship and has to adapt to their way of life. He might share his knowledge of the magical world with the members, like teaching them about potions that could heal wounds faster. And his presence could change the group dynamics, adding a new element of magic to their quests.
It could be Voldemort. Imagine if he somehow found a way to cross over into the world of the Fellowship. He would be a powerful and menacing antagonist, using his dark magic to oppose both Harry and the Fellowship.
She might bring her intelligence and magic skills to the group. For example, her vast knowledge of spells and potions could help the fellowship in various dangerous situations. She could also use her logical thinking to solve problems that the others might overlook.
Well, one possibility is that Harry discovers a new sense of purpose and discipline in the military. He might face challenges like tough training, and make new friends who help him grow as a person.
Maybe Harry joins the Wizengamot to bring about some long - awaited reforms. He could use his unique experiences to fight against the old - fashioned rules and biases within the magical government.
Well, it could be about Harry Potter finding a way to enter Tom Riddle's world in the fanfiction. Maybe he's on a mission to change Tom's path to the dark side.
Well, it could be that Harry joins the army because he feels a need for a new purpose in life. The story might show him adapting to the strict military discipline. Maybe he'll be part of a special unit and be involved in some sort of mission to save the world in a different way than he did before. For example, instead of using magic directly, he might use his strategic thinking and leadership skills he's developed over time.
In a 'harry joins voldemort fanfiction', perhaps Harry discovers a dark secret about the wizarding world that makes him think Voldemort was right all along. It could be something about the Ministry of Magic being corrupt and Voldemort's way of ruling, although extreme, is the only solution. So he joins Voldemort to 'fix' the wizarding world.
Well, it could be about Harry Potter exploring a new world of magic within the coven. Maybe he discovers new spells or magical abilities that are different from what he learned at Hogwarts. He might also meet new and interesting characters who have their own unique magical practices.
Well, perhaps Harry gets tired of being constantly in danger and feeling unappreciated in the wizarding world. He might be lured by the Dark Side with promises of power and safety. Voldemort could offer him a place by his side, showing him a different view of magic that seems more appealing in a warped way.
Well, perhaps in this fanfiction, Harry discovers his animagus form and the Dark Side somehow convinces him that his unique ability can be better utilized there. Maybe they promise him power and a new understanding of magic that the 'good side' has been suppressing.