Perhaps the fanfiction could explore how keeping an enemy closer affects the character's relationships with their friends. They might have to keep secrets from their friends, which could lead to some tense and interesting situations. For example, if Harry Potter were to befriend Draco Malfoy secretly, Ron and Hermione would be very suspicious and it could create a rift in their trio.
Another plot idea could be that the 'keep your enemies closer' situation leads to a character's redemption arc. The enemy, when befriended and understood better, starts to change their ways. This could show that in the Harry Potter universe, not all those who seem bad are truly so, and that friendship and understanding can bridge the gap between different houses and ideologies.
Harry Potter himself could be the main character. Given his history with Voldemort and his Death Eaters, it would be interesting to see him try to get closer to an enemy to gain an upper hand in the fight against the Dark Arts.
One idea could be a story where the reader gets to choose whether Harry joins a secret magical society within Hogwarts that is dedicated to uncovering ancient spells. Another could be a plot where the reader decides if Harry follows a different path in his search for Horcruxes, like exploring a hidden underground lair in the Forbidden Forest.
One idea could be that Harry discovers a hidden room in Hogwarts that leads to different magical realms. He has to choose which realm to enter first. Another is that he gets the chance to change a major event in the wizarding world's history through his choices.
A great plot for a Potter Manor fanfiction could involve a mystery that surrounds the manor. For instance, strange noises at night lead Harry to uncover a long - forgotten chamber. It could also be about Harry restoring the manor to its former glory, perhaps with the help of Hermione's research on ancient magic used in the construction of such manors.
Well, perhaps Harry uses a time - turner that has been magically enhanced to travel far enough back. He could disguise himself and befriend his parents, subtly guiding them to safety. Or he could change the circumstances of their meeting, for example, if he makes sure that they meet in a more secure place. Also, he could try to influence the actions of the Marauders so that they are more vigilant in protecting his parents.
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 traveler could be from a different magical realm entirely and come to the Harry Potter universe. They bring with them unique magical abilities that both fascinate and frighten the wizards in the Harry Potter world. This could lead to a series of adventures where they either share their knowledge or are hunted down by those who fear the new magic they possess.
One idea could be that Hecate, being the goddess of magic, takes Harry Potter under her wing secretly to teach him ancient and powerful magic that Dumbledore doesn't know. This could lead to Harry having new abilities to fight Voldemort.
A possible plot in Harry Potter Planeswalker fanfiction is that a Planeswalker accidentally brings a dangerous creature from another plane into the Hogwarts grounds. This causes chaos as the teachers and students have to figure out how to deal with it. It could also be that a Planeswalker has a special connection to the magic in the Harry Potter world, like being able to sense the presence of magic in a way that wizards can't. They could use this ability to discover hidden secrets about Hogwarts or the wizarding families. Maybe a Planeswalker is on a quest in the multiverse and the Harry Potter world is just one stop on their journey, and their actions in the wizarding world have consequences for their overall mission.
One interesting plot could be a time - travel story in the Harry Potter wonderland. For example, a character goes back in time to the Marauders' era and gets involved in their adventures, while also trying to prevent a future disaster in the wizarding world. Another idea is a story where a new, powerful magic is discovered in the wonderland, and Harry and his friends have to figure out how to control it before it falls into the wrong hands. A third plot could be about an alternate reality where Voldemort won the war, and the remaining good characters have to find a way to reverse the situation in the harry potter wonderland.