Well, perhaps a story where some witches and wizards from different houses are transported to a parallel magical world that is in a state of chaos. The magic there is unstable, and they need to figure out how to get back home while surviving attacks from rogue magical beings. They might also have to find a way to cooperate despite their house differences, which adds an interesting layer to the survival aspect.
One idea could be exploring what would happen if Harry had a twin sister who was sorted into Slytherin. It would add a whole new dynamic to the story, with her having different views and friends than Harry. She could be caught between loyalty to her house and loyalty to her brother.
Perhaps in this fanfiction, there could be a group of magical bats that are guardians of an ancient Hogwarts secret. Harry, as he befriends them in his bat form, gets drawn into this mystery. These bats could have their own language and culture that Harry has to learn. For example, they might communicate through a series of ultrasonic sounds that only a bat - like Harry - can understand. This could lead to a whole new adventure for Harry, separate from the main battles against Voldemort but still relevant to the overall protection of the wizarding world.
One unique plot idea is time - travel. For example, a character going back in time to change a crucial event in the wizarding world. Another is the idea of a Muggle - born wizard creating a new form of magic that combines Muggle technology and wizardry. And there are also stories where characters from different Hogwarts houses have to team up in unexpected ways to face a common threat.
A plot idea could be that a group of Hogwarts students accidentally travel to the Avatar world. They are then forced to learn bending in order to survive and find their way back home. Along the way, they discover that there are some similarities between magic and bending, like how both require focus and discipline.
One unique plot idea could be a time - travel scenario where Harry goes back in time and has to work with Lily to prevent Voldemort's rise without changing too much of the future. Another could be an alternate universe where Lily survives and she and Harry have to face new threats together.
Well, you could get a tattoo of a character from the fanfic in a unique pose or situation that didn't happen in the original books. For instance, if the fanfic has a scene where Harry Potter is using a new kind of magic, you could get a tattoo of him doing that. Or perhaps a tattoo of the fictional location in the fanfic that was really well - described and has a special place in your heart.
In some fanfics, there's a plot where Tom Riddle and Harry Potter are part of a magical experiment that binds their fates together. This causes them to share emotions and thoughts, which leads to some really interesting character development for both of them. Another unique idea is that Harry discovers a long - lost spell that can transfer the essence of one wizard to another, and in an attempt to save the wizarding world from a new threat, he transfers some of Tom Riddle's essence into himself to better understand his enemy. There are also fanfics where Tom Riddle is resurrected in a new form that is neither fully good nor bad, and Harry has to decide whether to trust this new Tom or not.
How about a story where the magic in the Harry Potter world starts to fade, and they seek the help of Naruto and his chakra - based powers? Naruto then tries to find a way to restore the magic, and in the process, they discover a hidden connection between the two worlds that was long forgotten. This would involve a lot of exploration, both in terms of the physical worlds and the magical concepts in both universes.
A unique plot could be that the Issa Brothers have a special power that can break dark magic spells in the Harry Potter universe. They use this power to help Harry and his friends when they are trapped by Voldemort's dark magic.
One unique plot idea could be that Lily Evans is somehow able to communicate with Harry through a special magical object. For example, a mirror that was enchanted by Lily long ago. This could allow her to give him advice and guidance during his adventures at Hogwarts. Another idea is that Lily's ghost lingers in a way that only Harry can see, and she helps him uncover secrets about the wizarding world that were lost over time.