Maybe it could be considered so because of the magic theme. Merlin is well - known for his magic, and in 'Harry Potter', magic is everywhere. The idea of a powerful wizard guiding the fate of others, like Dumbledore in 'Harry Potter' could be seen as similar to Merlin's role in his stories. But this is a very loose connection.
It's a tenuous link at best. If we consider that Merlin represents the archetype of the wise and powerful wizard, then Dumbledore in 'Harry Potter' could be seen as a similar figure. And the use of magic for good or evil in both could be a point of connection. But 'Harry Potter' has its own unique mythology. The Hogwarts houses, the Deathly Hallows, and the complex relationships between characters are all things that set it apart from being just Merlin fanfiction.
One way 'Harry Potter' might be considered Merlin fanfiction is in the way magic is portrayed. In both, magic is a hidden world within the normal world. Also, the idea of a prophesied hero, like Harry Potter, is similar to the idea of Merlin having a special destiny. However, 'Harry Potter' has developed its own lore and characters that make it a far cry from a simple Merlin fanfic.
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.
Well, in some fanfictions, Harry Potter might be seen as more powerful than Merlin because Harry has faced and defeated Voldemort. That's a huge accomplishment. Merlin, while very powerful in his own right, didn't have to deal with a dark wizard as complex and powerful as Voldemort. Harry's ability to survive the Killing Curse as a baby also gives him a sort of 'chosen one' status that could be seen as making him more powerful.
It's really not a typical Greek Titan fanfiction. But if we force the connection, we could look at the family lines in Harry Potter. Some families have a long and powerful lineage, much like the Titans were part of an ancient and powerful family of deities. However, this is a very tenuous connection as the Potter family's story and the way magic is passed down is unique to the world J.K. Rowling created.
Popularity of Merlin as Harry Potter fanfiction is a bit of a mixed bag. On some fanfiction websites, there are a decent number of stories that fall into this category. But in the grand scheme of things, it doesn't have the same level of popularity as, say, a typical Harry Potter fanfiction that stays true to the original series' characters and settings. It attracts those who are interested in exploring the crossovers between two magical universes, but it's not as widespread as other forms of Harry Potter - related fan works. There are probably fewer authors writing this type of fanfiction compared to more common Harry Potter fanfiction themes.
In Harry Potter fanfiction, Merlin can be depicted in many ways. Sometimes he's a benevolent figure, guiding the protagonists from the shadows. Other times, he might be a more complex character with his own motives and secrets. He could be presented as the originator of certain spells or magical techniques that are either lost or only partially understood in the main Harry Potter story. And his appearance might be described as a majestic figure draped in robes and surrounded by an aura of ancient magic.
Yes, there are likely some fanfictions out there with this concept. The idea of Merlin reincarnating as Harry Potter combines two very popular magical universes. It allows for a lot of interesting plot twists and character development. Writers might explore how Merlin's ancient magic and knowledge would manifest in the modern world of Harry Potter, and how it could change the course of the story we know.
The characters could interact in various ways. For example, Merlin could meet Hermione. Hermione, being very interested in magic knowledge, would be fascinated by Merlin's different approach to magic. She might ask him a million questions about his spells and how he learned magic in his time.
It could start with a magical event in the Harry Potter world that triggers the time travel. For example, a malfunctioning Time - Turner. Then the main character(s) from Harry Potter find themselves in Merlin's time. They could encounter Merlin himself and start learning about his magic. As the story progresses, they might face challenges in Merlin's world that can only be solved with their knowledge from the future. And at the end, they find a way to return to their own time, but with newfound knowledge and skills.
Merlin might start by teaching Harry the basics of magic from a different perspective. Maybe he would show Harry how to draw magic from the very essence of nature. For example, instead of using a wand in the traditional way, he could teach Harry to use his hands and the energy around him.
Merlin could help in Harry Potter fanfiction by being a sort of spiritual guide. Since he is a very well - known and powerful wizard in wizarding lore, his name and deeds could inspire the characters. He might appear in dreams or visions to Harry, Hermione, or Ron, guiding them on their quests, like how to find a hidden Horcrux or the true nature of Voldemort's power.