Hermione is often a very popular character. She's known for her intelligence and resourcefulness, and in fanfiction, she might come up with new spells or strategies to help Harry in his fight against Voldemort.
One interesting plotline could be an alternate universe where Harry and Voldemort have to team up against a greater evil. This flips the traditional dynamic on its head.
One great Snape vs Voldemort fanfiction is 'The Dark Mark's Secret'. It delves into Snape's complex relationship with Voldemort. Snape is constantly in a precarious position, having to play the double agent. The story shows how he uses his wits against Voldemort's brute power. Another one is 'Snape's Hidden Alliances'. It focuses on how Snape manages to outmaneuver Voldemort in some crucial situations. The characterizations are really well - done in both of these, making them engaging reads.
One interesting plot twist could be that Voldemort actually has a change of heart. Maybe in the fanfiction, he realizes the futility of his dark ways after seeing the strength of Harry's love and friendship. Another could be that Harry discovers a new, unexpected power within himself that is not related to his typical Gryffindor courage or his connection to Voldemort's soul pieces. For example, he might find he has the ability to manipulate time in a way that gives him an edge in the battle.
Harry often becomes more conflicted. He has always seen Voldemort as the ultimate evil, but now being mates, he has to re - evaluate his views. He might start to see the humanity in Voldemort, which makes him question his own beliefs and actions in the fight against the Dark Lord. For example, he may hesitate in battles more than before.
Often in fanfiction, their relationship can change drastically. They could end up as allies, which would require both of them to change. Harry would have to see past Voldemort's evil deeds, and Voldemort would have to let go of his hatred for Harry. This exploration of character change makes fanfiction so interesting.
The Gryffindors, of course, are usually very vocal in their support of Harry. They might cheer him on, offer their own magical skills if they can, and be ready to fight alongside him. The Slytherins can have a more complex reaction. Some might side with Voldemort out of fear or ambition, but there could also be Slytherins who see the wrong in Voldemort's ways and secretly support Harry. The Hufflepuffs would likely be focused on protecting the innocent within Hogwarts and providing a sense of stability and comfort during the chaos. And the Ravenclaws might be analyzing the situation, coming up with strategies to help Harry or trying to understand the deeper magic at play in the battle.
The main thing that makes Snape vs Voldemort fanfiction interesting is the contrast between the two characters. Snape is complex, with his own motives and a hidden side. Voldemort is pure evil. So when they interact, there are always mind games and power plays. For example, Snape has to constantly deceive Voldemort, and the tension this creates is exciting.
Well, in a fanfiction, a plotline could be that Percy Jackson is on a quest and somehow crosses paths with Voldemort. Voldemort senses Percy's power and wants to study it. Percy, not knowing much about the wizarding world, initially mistakes Voldemort for just another monster. As they interact more, they realize that their worlds are more intertwined than they thought. Another plot could involve a powerful artifact that both of them are after. The artifact has the power to change the balance of both their worlds. So they are in a race against each other to get it, but along the way, they start to understand each other's motives and might even consider working together to keep the artifact out of the wrong hands.
Their interaction would be intense. Merlin, being from a different era and having a different view of magic, would likely be appalled by Voldemort's use of dark magic. Voldemort, on the other hand, would probably see Merlin as a threat to his power. Merlin might try to reason with Voldemort at first, but when he realizes that Voldemort is beyond redemption, he would use his magic to stop him.