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 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.
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.
Another power could be the ability to communicate with magical creatures on a deeper level. Since Merlin was said to have a great understanding of all things magical, the heir in fanfiction might be able to gain the trust and cooperation of creatures like centaurs and unicorns more easily than others.
Power and responsibility is a big one. Since the character has a connection to Merlin, they have to deal with the power that comes with it and the responsibility to use it well. Also, the exploration of ancient magic and how it fits into the existing Harry Potter magic world is quite common. For instance, they might explore how Merlin's magic is different from what is currently taught at Hogwarts. There could also be themes related to prophecy and destiny, as the character's new identity as the Heir of Merlin may be tied to some greater purpose in the wizarding world.
Well, it depends on the specific fanfiction. Some fanfiction authors might create a really elaborate backstory where Harry Potter is somehow related to Merlin as an heir. They could base it on things like similar magical abilities, a prophetic connection, or a hidden bloodline. However, not all fanfictions follow this concept. There are many different takes on Harry's story in the fanfiction world, and this is just one of the more imaginative ones.
Another possible candidate in fanfictions could be Neville Longbottom. He has a deep connection to the magical world and shows great courage and growth throughout the series. His latent magical abilities, which are finally fully realized, could be interpreted as him being an heir of Merlin in a way. He has the potential to be a great wizard, just like Merlin was.
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.
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.
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.
One common theme is the discovery of hidden powers. Since Harry is Merlin's heir, he often uncovers abilities that were previously unknown to him, like advanced spell - casting or magic related to nature.