In some fanfictions, it could be descendants of minor characters from the original Harry Potter series. For instance, the grandson of Hagrid might be drawn to the Hidden Island to continue Hagrid's love for magical creatures. He could be one of the main characters, trying to protect the unique and endangered species on the island. Also, there might be a group of students from Hogwarts who get lost during a field trip and end up on the Hidden Island. Among them, a character like Hermione - like girl, intelligent and resourceful, would take the lead in trying to figure out how to get back and in the process, uncover the island's secrets.
Sometimes, it's characters who have a special connection to the island's magic. Maybe a young wizard who has a rare magical ability that is linked to the power source of the Hidden Island. This character, let's call him Ethan, might be sought after by both good and bad forces because of his connection. He then becomes one of the main characters as he battles to protect the island and its secrets from those who would misuse the magic there.
Harry Potter himself is often a main character in such fanfiction. He might be the one to discover or be given the special armor. Hermione could also be involved, perhaps using her intelligence to study and improve the armor's magical properties.
There could also be a mysterious ancient wizard who is long forgotten in the regular wizarding history but is central to the Primal Magic story in the fanfiction. This wizard might have been the first to discover or master Primal Magic and left behind clues or artifacts that the main characters in the fanfiction are now trying to uncover.
Harry Potter himself is often associated. Since he has a connection to the phoenix Fawkes in the original series, it's likely that in fanfiction involving a phoenix hybrid, he might play a role in discovering or befriending the hybrid. Hermione could also be involved as she is always curious about new magical phenomena and would surely be interested in a phoenix hybrid.
Harry Potter himself could be one of the main characters associated with dragon armor. He's always getting into dangerous situations, and dragon armor could be something he discovers on one of his adventures. Another could be Hermione. With her love for knowledge, she might be the one to research about the armor's history and properties.
Harry Potter himself is often associated with it. After all, he's the main character in the original series and it makes sense for him to be connected to the legendary sword in fanfictions. He could use it to fight Voldemort in new and exciting ways.
Ron Weasley also plays an important role. His loyalty to Harry and his own knowledge of the wizarding world, especially the Weasley family's traditions, could provide valuable insights. He might be the one to support Harry emotionally during the difficult process of dealing with the revelations of his hidden inheritance, and also offer practical help in certain situations.
In a lot of 'Harry Potter desert island fanfiction', the main characters are Harry, Hermione, and Ron. But there are also some that focus on Draco Malfoy. It's interesting to see how he would interact with the others in such a difficult situation. His Slytherin nature might clash with the Gryffindors at first, but then they might have to work together to survive, which makes for a great character development story.
There are some original characters in Harry Potter fanfiction that are associated with mind control. For example, a new dark wizard who has emerged from a hidden part of the wizarding world. This character might have developed a unique form of mind control that combines magic with some form of ancient mind - bending techniques. And then there are the students in fanfics who might discover or be forced into learning mind - control magic, and they become associated with it as they struggle with the moral and practical implications.
There might be a forgotten or background character from the original series who is given super speed in the fanfiction. For example, Neville Longbottom could be an interesting choice. His growth throughout the original series could be further enhanced with super speed. He could use it to protect his friends and Hogwarts in unexpected ways, becoming a hero in a different sense compared to his original character arc.
Dumbledore is often a main character in Harry Potter 1945 fanfiction. Since he was around during that time, many stories explore his youth, his friendships, and his early battles against the dark forces.