One possible plot could be that the Kubikiribocho, the sword in Naruto, somehow finds its way into the Harry Potter universe. Harry discovers it during one of his adventures in the Forbidden Forest. He initially has no idea how to use it but gradually realizes it has some unique powers that can be harnessed against Voldemort. For example, it might be able to cut through dark magic spells. However, there are also some negative aspects to the sword as it tries to corrupt Harry a bit, just like the influence of the Horcruxes. Harry has to fight against this internal battle while also using the sword's power to defeat Voldemort.
Maybe the Kubikiribocho is a hidden relic in Hogwarts that was placed there long ago by a wizard who had visited the Naruto world. Harry stumbles upon it while exploring a secret chamber. The sword has a mind of its own and chooses Harry as its wielder. It gives Harry the ability to see the true forms of dark creatures, which helps him in his fight against Voldemort's Death Eaters. But it also has a thirst for blood, so Harry has to learn to control this aspect of the sword to use it for good without becoming a dark wizard himself.
Hermione could study the Kubikiribocho. She would pour over books in the Hogwarts library to figure out its origin and powers. Harry, on the other hand, might be the one to actually pick it up and test its abilities in combat. Ron could be a bit skeptical at first but would come around when he sees the sword's potential against the dark forces. For example, the sword might react differently to different spells cast at it. Harry could learn to use these reactions to his advantage in battles.
One idea could be exploring the origin of the Kubikiribocho. Maybe it was crafted by a long - forgotten clan with special powers, and Naruto discovers hidden inscriptions on it that lead him to a new jutsu. Another could be a story where Naruto has to fight an enemy who has also mastered the use of a similar - looking weapon, and through the battle, he learns new ways to use the Kubikiribocho.
One interesting plot idea could be exploring what would happen if Harry had a different upbringing, like being raised by the Malfoys. It would completely change his view of the wizarding world and his relationships. Another idea might be a time - travel fanfic where Harry goes back to the Marauders' era and interacts with his parents and their friends. This could lead to him preventing certain tragedies or changing the future in unexpected ways. And then there's the concept of a fanfic where the roles are reversed, and Voldemort is the one trying to protect the wizarding world from a greater evil, with Harry being the main antagonist.
A great plot point might be Arwen's perspective on the concept of magic in the Harry Potter universe compared to that in Middle - earth. Since she has a different understanding of magic, her reactions and interactions with the wizards could be really fascinating. For instance, she might be surprised by some of the more 'brute - force' spells used in the wizarding world, while the wizards might be in awe of her more subtle and nature - based elven magic. Another interesting aspect could be if Arwen gets involved in the fight against Voldemort. Her elven wisdom and powers could potentially change the course of the battle in unexpected ways.
Well, perhaps the Omnitrix gets mixed up with the magic in Hogwarts. It starts malfunctioning and instead of the usual alien forms, it gives Harry forms of ancient wizards. He has to figure out how to control these new forms while also dealing with the mystery of why the Omnitrix is acting this way. And he might learn new spells and magic from these wizard forms.
One idea could be that Palpatine somehow discovers the wizarding world of Harry Potter. Maybe he sees it as a new realm to conquer. He could try to manipulate the Ministry of Magic using his Sith mind - tricks, and Harry Potter would have to figure out who this strange new threat is and stop him. It would be a clash of two very different kinds of magic.
Maybe in the 'Harry Potter in Undertale fanfiction', Harry discovers that Voldemort has also found his way into the Undertale world and is trying to gain power there. Harry has to learn the rules of this new world quickly. He befriends Sans and Papyrus. Sans, with his knowledge of the resets in Undertale, helps Harry understand how to manipulate time in a way that could give him an edge against Voldemort. Papyrus, on the other hand, is enthusiastic about Harry's magic and they train together to fight off Voldemort's minions in the Undertale world.
Yes, often there are. For example, the main character as a descendant of Merlin might have unique magical powers. They could be able to perform spells that are long forgotten or have an innate understanding of ancient magic. This can lead to all sorts of adventures, like exploring hidden chambers in Hogwarts that were sealed by Merlin himself and uncovering secrets that could change the wizarding world.
Maybe a dark wizard in the Harry Potter universe has found a way to access the power of the One Ring from Middle - earth. Aragorn, sensing the danger, travels to the wizarding world with the help of some elvish magic. He teams up with Harry Potter to stop the dark wizard from using the Ring's power. Along the way, they face many challenges, including dealing with the corrupting influence of the Ring on those in the wizarding world who are power - hungry.
Another plot could be that Voldemort discovers Powergirl's existence and sees her as a threat. He tries to manipulate the wizarding world against her. But Harry and his friends believe in her and together they work to expose Voldemort's lies and also learn from Powergirl about different ways of fighting evil. Powergirl could introduce new concepts of justice and heroism to the wizarding world.