Well, perhaps Harry is on a quest in the wizarding world and accidentally stumbles upon a portal to Atlantis. In Atlantis, they have a different form of magic which Harry has to learn quickly. He uses his quick - learning ability, which he has shown at Hogwarts many times. As he masters the Atlantean magic, he earns the respect of the people. He might also find some ancient magic artifacts there that are related to his own past or to the history of magic in the wizarding world. This could lead to him gradually taking on a leadership role and becoming the ruler.
One possibility is that Harry discovers a hidden magical connection between Hogwarts and Atlantis. Maybe he is magically transported there and through his unique powers from Hogwarts, he begins to assert his influence. For example, he could use his knowledge of spells to solve problems in Atlantis that the local wizards or mages couldn't. Another aspect could be that he uncovers a dark secret in Atlantis related to the Dark Arts, and he has to use his Gryffindor courage to face it and in the process, becomes a respected figure and eventually the ruler.
One possible main antagonist could be an Atlantean sorcerer who is jealous of Harry's growing influence and power in Atlantis. This sorcerer might have his own plans to rule Atlantis and sees Harry as a threat. Another could be a group of traditionalist Atlanteans who oppose any foreign influence, like Harry's, and they try to undermine his attempts to bring new ideas and magic from Hogwarts.
Maybe Harry discovers he has some hidden connection to Atlantis. He could be magically transported there and due to his powerful magic and heroic nature, he ends up becoming the king. He then has to deal with Atlantis's internal politics and protect it from external threats.
One possible plot is that Voldemort also has an interest in Atlantis. Harry, as the King of Atlantis, has to not only protect his new kingdom but also prevent Voldemort from getting his hands on Atlantean power sources. This could lead to epic battles underwater, with Harry using his Patronus and other spells against Voldemort's dark magic, all while trying to uphold the traditions and values of Atlantis.
Well, it could be about Harry Potter becoming the ultimate ruler of the magic world. Maybe he discovers some ancient magic that gives him the power to control all aspects of magic, from Hogwarts to the Ministry of Magic. He might use this power to bring about a new era of peace and harmony among wizards and witches, while also dealing with the dark forces that still lurk in the shadows.
Maybe Harry is sent on a mission by Dumbledore. Dumbledore has received some strange prophecies that seem to be related to Atlantis. Harry, along with his friends Hermione and Ron, travel to Atlantis. Once there, they find that the magic in Atlantis is different but related to their own. They have to figure out how to work with the Atlantean magic to stop an ancient evil that has been awakened and is endangering both Atlantis and the wizarding world. It could involve a lot of exploration of the Atlantean culture and magic system, which would be really fascinating.
In a fanfiction where Harry Potter is raised in Atlantis, his relationships would be quite different. He would make friends among the Atlanteans, who could have their own unique cultures and appearances. His relationship with Hogwarts would be complicated. He might not feel as attached to it as he did in the original story, or he could bring Atlantis - influenced ideas to Hogwarts, creating a new kind of magic there.
One idea could be that Hogwarts students discover a hidden portal to Atlantis during a Care of Magical Creatures class in the Forbidden Forest. They then have to navigate the ancient Atlantean society, which has its own form of magic. Maybe they need to team up with Atlantean wizards to defeat a common dark force that threatens both their worlds.
Yes, there are likely some fanfics out there that blend the two. Some fans might be intrigued by the idea of Harry Potter characters exploring the lost city of Atlantis, with its own unique magic and secrets. It could involve Harry and his friends on a quest in Atlantis, facing new challenges and perhaps even learning new types of magic.
It could be portrayed as a dangerous quest. Harry might have to overcome many obstacles to reach Atlantis, like sea monsters or magical storms.
One common theme is the exploration of ancient magic. Since Atlantis is often associated with powerful and mysterious magic, in fanfiction it can be combined with the known magic in Harry Potter. Another theme is adventure. Characters usually embark on a journey to Atlantis, facing various obstacles along the way.