Perhaps the fem Sauron has a goal of obtaining a powerful magical artifact in the Harry Potter universe, like the Philosopher's Stone or a Horcrux. She teams up with some of the darker forces in the wizarding world, like Death Eaters. Harry Potter, along with his friends, has to stop her. They might discover that some of the magic in the Harry Potter world can counteract the dark powers she brings from Middle - earth.
In this fanfiction, the fem Sauron could be a fallen witch from Middle - earth who was banished and ended up in the Harry Potter universe. She decides to create her own army of dark wizards. Harry Potter, being the hero, tries to prevent her from recruiting more followers. He might learn some new forms of magic from her in the process of their encounters, but also has to be careful not to be corrupted by her dark influence.
One possible plot could be that the fem Sauron, with her dark powers, infiltrates Hogwarts. She could initially be disguised as a new student or a teacher. Harry Potter senses something is off about her. There could be a series of magical duels and battles of wits between them as Harry tries to expose her true identity while she tries to carry out her own evil plans within the wizarding world.
One possible plot could be that Sauron somehow manages to enter the wizarding world. Maybe through a powerful dark magic spell that links the two universes. Harry, being the hero, senses the new and greater evil. He then has to figure out how to defeat Sauron, which is much more difficult than any foe he has faced before. He might have to learn about the power of the One Ring and how to destroy it, all while protecting Hogwarts and the wizarding world from Sauron's dark minions.
Well, one possibility could be that Harry discovers his true parentage as Sauron's son in a very shocking way. Maybe through some dark magic revelation. Then he might struggle with his identity, being a part of the wizarding world that he loves but also having this dark connection. He could face a lot of inner turmoil as he tries to decide whether to embrace his dark heritage or fight against it.
A possible plot is that there's a magical experiment gone wrong at Hogwarts that creates a portal to Danny Phantom's world. A female Danny Phantom enters the Harry Potter world through this portal. The Ministry of Magic thinks she's a threat at first, but she proves herself useful when a new dark force emerges. She teams up with Harry and his friends, using her intangibility and other powers to their advantage in battles and sneaking around the castle.
In a 'Harry Potter x fem Bowser' fanfiction, it could be that fem Bowser is a part of a prophecy in the Harry Potter world. The prophecy states that a powerful being from another realm will come to either save or destroy the wizarding world. Harry and his friends are initially skeptical but soon realize that she has her own reasons for being there. She could be on a quest in her own world that has some connection to the events in the Harry Potter universe, and together they must figure out how to use her presence to their advantage.
One possible plot could be that fem Lucifer, being intrigued by the magic in the Harry Potter world, decides to visit Hogwarts. She might get involved in the fight against Voldemort, using her own powers which are different from the magic in the wizarding world. This could lead to a lot of interesting interactions between her and the main characters like Harry, Hermione, and Ron.
One interesting plot could be that the fem Naruto character is on a quest to find a way to return to her own world. Along the way, she teams up with Harry Potter and his friends. She uses her ninja skills to help them fight off dark wizards, and in return, they help her figure out the magic needed to get back home.
One possible plot could be that the fem Harry Potter arrives in Westeros with her magical abilities. She might get involved in the power struggles between the different houses. For example, she could use her magic to help a particular house gain an advantage in a battle, perhaps by creating illusions to deceive the enemy. Her unique brand of magic, different from the magic known in Westeros, would both amaze and frighten the people there.
A plot could be that in a post - war Hogwarts, fem Harry Potter is looking for a new purpose. She discovers a way to cross dimensions and ends up in the world of the Avengers. Clint Barton is intrigued by her and her magic. They form a bond as they try to figure out how to stop a dark force that is threatening both of their worlds. There could be a lot of cultural clashes and misunderstandings at first, but as they get to know each other better, their relationship deepens.
One idea could be that the heir of Sauron somehow infiltrates Hogwarts under a false identity. He tries to use the chaos of the wizarding world to his advantage to gather power. Another could be that there is a prophecy that links the heir of Sauron with Harry Potter, and they must either fight or unite depending on how the story unfolds. Or perhaps the heir of Sauron is actually a long - lost relative of one of the Hogwarts professors, which adds a layer of mystery and conflict.
One possible plot could be a fem Naruto being somehow transported to the Harry Potter world. She might initially struggle to understand the magic system there as it's so different from chakra. But her ninja skills could come in handy, like her stealth and combat abilities. For example, she could help Harry and his friends during a dangerous mission at Hogwarts by using her unique fighting style.