Maybe there's a plot where a master assassin in the Harry Potter world has to hunt down a rogue wizard who is using dark magic to create chaos in the Muggle world. The assassin has to navigate both the wizarding and Muggle worlds, using their skills and knowledge of both to complete the mission. This would bring a whole new dynamic to the story as they deal with different laws and cultures in both worlds.
One interesting plot could be that the main character, who has assassin skills, is secretly protecting Hogwarts from a new and unknown dark threat that the regular wizards can't detect easily. They use their unique combat skills along with magic to keep the school safe.
One interesting plot could be an assassin who is secretly a double agent within Voldemort's ranks. They pretend to be working for him but are actually protecting Harry Potter and his friends.
One interesting plot could be a character using arithmancy to predict the return of a dark force. They might discover hidden patterns in numbers related to past dark events and use that knowledge to try and prevent a new threat.
One interesting plot could be Harry discovering a new, hidden magical ability that was not part of the original books. For example, the power to communicate with magical creatures on a deeper level. Another plot might involve Harry traveling to a different magical dimension where the rules of magic are completely different. He would have to adapt and use his skills in new ways.
Maybe in the fanfiction, Harry becomes the master of alchemy and uses it to create magical potions with extraordinary powers. For example, he might create a potion that can temporarily give students the ability to speak to animals, which leads to all kinds of adventures as they communicate with the magical creatures around Hogwarts.
Maybe the assassin master has a hidden past related to Naruto's family. So, the story could revolve around uncovering this mystery while Naruto trains under him. This would add depth to Naruto's character development as he learns about his family's secrets.
Well, some fanfictions might have a plot where the dark arts master has a unique connection to an ancient and powerful dark magic artifact. This connection could drive the story as the character tries to either master the artifact's power or keep it from falling into the wrong hands, all while dealing with the challenges in the Harry Potter universe like avoiding the Ministry of Magic's detection.
One interesting plot could be Harry Potter discovers his hidden talent for blade mastery in a secret chamber at Hogwarts. He starts training with a magical blade that has special powers. Maybe it can cut through dark magic spells. Another plot might be that he uses his blade master skills to defend Hogwarts during an attack by a new dark force.
One interesting plot could be that Harry Potter, as the Master of Death, encounters Aphrodite in the wizarding world. Maybe Aphrodite is intrigued by the concept of death in the wizarding realm and wants to learn more. Harry, in turn, is fascinated by her powers of love and beauty. They could team up to help a young wizard who has lost all hope and love due to a dark magic curse, with Aphrodite using her love - inducing powers and Harry using his mastery over death to free the wizard from the curse's hold on his soul.
In some Harry Potter 8 fanfictions, there are plots where the characters continue to face new dark magic threats. For example, a new dark wizard might emerge, and Harry, Hermione and Ron have to use their combined skills and knowledge to defeat this new foe. Another plot could be about the exploration of the wizarding world's past in more depth, revealing secrets that were previously unknown.
One common plot could be revenge. Maybe she's out to avenge the death of someone she loved, using her assassin skills. Another could be that she's part of a secret organization that uses her unique position as Harry Potter to achieve their assassin - related goals.