Harry Potter is the central character. There may be a wise old sea - turtle wizard who imparts important knowledge to Harry. Some sea - nymphs could be characters that either help or hinder Harry. Neville could also be part of the story, perhaps using his plant - based magic in a new way underwater to help Harry in his quest to be the king of the sea.
Well, it could be about Harry Potter discovering some hidden magical underwater kingdom. Maybe he has a special connection to the sea, like being able to communicate with sea creatures. He could then use this power to fight against dark forces that are threatening the sea world.
There might be a fanfiction where a character is both a Hogwarts student and has a secret identity as a sea king's heir. This character could struggle with balancing their magical studies at Hogwarts with their new - found responsibilities in the underwater kingdom. They might have to face challenges like preventing a war between the underwater and wizarding worlds.
Fanfiction.net is also a good place. There are numerous Harry Potter fanfictions there, and if you search specifically for 'Harry Potter Sea King' with some patience, you might come across some interesting pieces. However, the quality can vary greatly, so you may need to read a few to find the really good ones.
There could be some house - elves involved too. Maybe Dobby appears in the bathroom to offer Harry some help or advice, which would be a rather comical situation considering Harry is in the shower. Or other house - elves who are cleaning the bathroom while Harry is in there and he has some sort of interaction with them.
One possible plotline could be that Harry discovers he has a hidden heritage related to the Dragon King. Maybe his parents had some connection to the Dragon King's world that was kept secret, and now he has to figure out how to use this new - found knowledge and power to fight against Voldemort.
Perhaps there is a magical tournament in the wizarding world that is modeled after the jousts and challenges in King Arthur's court. Harry is forced to participate and as he does, he realizes that there are deeper connections between the values of the Arthurian era and the current state of the wizarding world. He then uses this knowledge to bring about positive change in the wizarding community.
He could meet the Dalton students. They might be very different from his Hogwarts friends, maybe more focused on academic magic in a different way.
Harry Potter might be a bit surprised. He'd probably think it's strange that people are writing about his friends' and his own relationships in such a different way. Hermione would likely be very interested in the writing style and how the authors are creating these new relationships. She might even take notes to improve her own writing. Ron would just laugh it off most of the time. He'd find it a bit odd but also funny.
Obviously, Harry Potter himself. There could also be a new character who is like a raven - guardian, someone who has been watching over Harry because of his raven heritage. And perhaps some old characters like Hermione and Ron might play a role in helping Harry understand his new identity.
Obviously, Harry Potter himself. Then there would be his friends like Ron and Hermione. They would be there to support Harry and also be amazed by his new powers. Dumbledore would surely be in the story as he is an important figure in Harry's life. And of course, the villains like Voldemort and his Death Eaters who would be the antagonists against Harry's newfound abilities.