In this fanfiction, Neville could be an important character. He might also show an interest in elemental magic and join Harry in his studies. There could also be a mysterious figure from the Forbidden Forest who has a connection to elemental magic. This figure could either be a help or a hindrance to Harry as he tries to master the new magic.
Besides Harry, there could be a character who is a descendant of an ancient elemental magic family. This character might initially be a rival to Harry in mastering the magic but later becomes an ally. Also, Dumbledore could play an important role. He might be secretly guiding Harry in his journey of learning elemental magic, using his own deep knowledge of the wizarding world's secrets.
Snape is a character that could play a major role. Given his past with dark magic, he might be a reluctant mentor to Harry, guiding him in understanding the power and danger of it. Dumbledore, too, would likely be in the story, as he is always concerned about Harry's well - being and actions.
One great plot development could be that the elemental magic Harry learns is not part of the traditional Hogwarts curriculum. So, he has to seek out hidden mentors or ancient texts. This could lead to him exploring parts of the wizarding world that are long forgotten. As he delves deeper into elemental magic, he might also start to question the limitations of the magic he has been taught so far at Hogwarts.
Obviously, Harry Potter himself is a very important character as the story revolves around him learning family magic. His friends like Hermione and Ron might also be important as they could support or help him in his journey of learning this magic.
There could be Hermione. Since she's always interested in learning new things, she might be involved in Harry's exploration of mysticism.
Obviously, Harry Potter is a main character as the title suggests. He is the one who is on the journey of learning wandless magic. Hermione Granger could also be an important character. She might be helping Harry research about wandless magic, using her vast knowledge from the library.
Maybe it could be an ancient magical being like a centaur. Centaurs are known for their knowledge of the stars and ancient magic. They might take Harry under their wing and teach him old magic that has been passed down through their generations.
Hermione would probably be involved. She could help Harry research about the island, like its history and any magical properties it might have.
It could be an older relative who was thought to be dead but actually has been living in seclusion, waiting for the right time to teach Harry about their family magic. This relative might have a vast knowledge of the family's magical traditions and spells.
Severus Snape is also a popular choice. His complex character and vast knowledge of magic can create interesting dynamics when he meets characters from different magical worlds. He could either be a mentor or an antagonist in these crossovers.
Besides Harry, Hermione is a key character. She can research and find loopholes in the Ministry's laws and regulations. Ron is there too, providing muscle and emotional support. Neville Longbottom could also be involved. He has grown into a strong and brave wizard, and he might join Harry's cause. Additionally, Luna Lovegood with her unique perspective on magic could offer different ways of approaching the conflict with the Ministry. Some fanfictions might also include Sirius Black, if set in a timeline where he didn't die, as he has a history of opposing the Ministry's unjust actions.