A plot device often used is the betrayal of a friend. In fanfiction, this can be a powerful way to make Harry feel alone. For instance, if Ron were to turn on Harry because of jealousy or some false accusation, Harry would be left feeling extremely alone. Also, the discovery of a hidden secret about his past that no one else seems to understand or believe can isolate him. He might find out something about his parents or his magical abilities that makes him an outcast even among those he thought were his allies.
The use of dark magic threats specifically targeting Harry can be a plot device for his loneliness. When he realizes that he's the sole target and that he can't fully trust others to protect him, he feels alone. For example, a new dark wizard might be after Harry and use spells to isolate him from his friends. He may find himself in situations where he has to face this danger alone, and the fear and loneliness would be palpable. This can also lead to him making decisions on his own, further separating him from the support system he once had.
One common plot device is the introduction of new characters who initially misunderstand Harry, which makes him feel more alone. For example, a new student might come to Hogwarts and, because of rumors or Harry's fame, avoid him or be unkind, adding to his sense of isolation. Another device could be the separation from his friends. Maybe there's a magical accident that sends Harry to a different dimension or a locked part of the castle where he's completely alone and has to figure out how to get back while feeling lonely and scared.
One common plot device is the discovery of ancient artifacts or prophecies that link Harry to Merlin. For example, a magical amulet that was once Merlin's might be found and react only to Harry. Another is the appearance of a character who knew Merlin in the past and recognizes Harry as his reincarnation.
A common plot device is misdirection. Harry might create a false lead or distraction that makes Snape focus on the wrong thing. For example, he could stage a minor 'accident' in the corridor that draws Snape's attention while he slips away to do something else he's not supposed to. Another device is using his friends' unique abilities. If Hermione has found a loophole in a rule, Harry can use that knowledge to outmaneuver Snape who is always strict about the rules.
A common plot device is the exploration of a hidden magical world related to Merlin. Harry, as the heir, is the key to unlocking this world. There might be new magical creatures, spells, and challenges there. He could also face opposition from those who fear his new power or those who want to use him for their own evil purposes. This creates conflict and tension in the story. Additionally, his connection to Merlin could lead to a rewriting of history or a new understanding of the origins of magic in the wizarding world.
One common plot device is the discovery plot. Midoriya might find out in a very dramatic way that Harry Potter is his father. For example, he could find a hidden letter or a magical object that reveals the truth. Another device is the mentor - like role of Harry Potter. Since he's so experienced in magic, he could teach Midoriya some special skills related to his quirk that has a magical origin.
Often, in these fanfictions, the discovery of a new, ancient and dark magic artifact can be a plot device. Harry might find this artifact and, as he tries to understand or control it, he starts to develop dark powers. Also, the idea of a prophecy misinterpreted can play a role. A prophecy that was thought to be about his heroism is actually about his fall to the dark side, leading him to explore and use dark powers.
The use of prophecies is also quite common. Similar to how there are prophecies in both Harry Potter and Game of Thrones, fanfictions might create new prophecies that involve characters from both worlds. For example, a prophecy about a character from Game of Thrones being the key to defeating Voldemort. This creates a sense of destiny and drives the plot forward. Also, the idea of hidden identities can be used, like a character from Harry Potter disguising themselves as a noble in Westeros and causing all sorts of chaos as their true nature and abilities are gradually revealed.
One common plot device is Fem Merlin being a time - traveler. She could come from the past or future to change certain events in the Harry Potter timeline. This can create a lot of interesting scenarios where she has to adapt to the modern wizarding world while also trying to achieve her mission.
One common plot device is time - travel. A character might go back in time and accidentally change something that makes Draco Harry's son. Another is a powerful magical curse or blessing that alters family relations. For example, a curse on the Malfoy family that can only be broken if Draco is 'adopted' into Harry's family in a magical sense.
One common plot device is the revelation of hidden powers. When a blood binding is involved, often characters discover new and unexpected magical abilities that are tied to the bond. For example, they might be able to communicate telepathically or share magic in unique ways.
One common plot device is the discovery of her royal lineage. It usually happens in a dramatic way, like finding a hidden letter or a magical object that reveals her true identity. Another is the conflict between her wizarding life and her new royal duties. She has to balance things like going to Hogwarts and attending royal functions. Also, there's often a love interest from the royal court, which creates a love triangle with her existing relationships in the wizarding world.