One common plot element is Harry's struggle with loneliness. Since he's immortal, he'll outlive all his friends and loved ones, which can lead to a sense of isolation.
A plot twist might be that Harry's immortality is the key to saving the Twilight world from a new, unknown threat. He might be the only one who can stop it because his magical immortality gives him abilities that the Twilight creatures don't have. Also, there could be a love triangle or some sort of complex relationship where Harry falls in love with a character from the Twilight series, but there are obstacles because of his different nature and the fact that he's from another world. And sometimes, the magic in the Twilight world is revealed to be related to the magic in Harry Potter's world in a way that no one suspected before.
One interesting plot element is the clash of magic systems. In Supernatural, magic is often more about spells and rituals from a hunter's perspective, while in Harry Potter, it's about wand - based magic. When these two meet, it creates a really unique dynamic. For example, seeing Sam try to figure out how to use a wand or Harry trying to understand the more ancient forms of magic the Winchesters use.
False accusations are very common. Usually, Harry is wrongly blamed for something he didn't do, like being involved in dark magic activities.
One common plot element is the discovery of the heir. It often involves a young wizard or witch suddenly realizing they have a connection to Grindelwald. Another is the struggle with the dark legacy. The heir may be conflicted about whether to embrace the power associated with Grindelwald or reject it. And there's usually some sort of conflict with the existing wizarding community, as they may be feared or mistrusted.
One common plot element is the reaction of the friends and family. In many of these fanfictions, Hermione and Ron might be shocked or supportive in different ways. Another element could be how the female Harry Potter deals with the challenges of being pregnant while still having to face the magical world's threats or her own identity issues.
Well, one plot element is the discovery of the sword - related power or ability. Maybe it's a magical sword he finds or a latent ability within him that he unlocks. Then there's the part where he has to keep it a secret at first, because it's so different from normal wizarding abilities. And of course, there are often battles where his swordsmanship gives him an edge over his opponents, making him a key player in the fight against the dark forces in the wizarding world.
The themes in 'Harry Potter is immortal' fanfictions usually include a search for purpose. Harry has an endless life, so he needs to find something meaningful to do. There is also the theme of change. While he doesn't age, the world around him does, and he has to adapt. And of course, the theme of mortality in contrast to his immortality. He is constantly reminded of the fact that everyone else is mortal, and this can create a lot of internal conflict within him.
Well, many fanfictions explore the supernatural aspect of prophecy in more depth. Instead of just the general prophecies in the books, they might have Harry being the center of a web of prophecies that are full of strange and otherworldly implications. Another popular element is the idea of Harry having a spiritual guide, like a spectral animal or an ancient wizard's spirit that helps him on his journey. And the transformation of normal wizard spells into something more supernatural, like a spell that can create a portal to a different dimension.
One common theme is the exploration of new powers. Since it's a female Harry Potter, often she has different or enhanced powers compared to the original male version. Another theme is the discovery of hidden parts of the wizarding world. The supernatural aspect usually leads to uncovering secrets. For example, there might be a hidden realm full of strange magical creatures.
The theme of the outsider is also prevalent. Characters from one universe are often the outsiders in another. For instance, when a character from Supernatural enters the world of Harry Potter, they have to figure out how to navigate a completely different society with its own rules and customs. This creates interesting situations where the character has to adapt, learn new skills, and form new relationships while still holding on to their own identity.