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.
In such a fanfiction, Harry might discover ancient spells that give him an edge in battles. For example, he could learn old defensive magic that can protect Hogwarts in a more powerful way than the existing spells. He might also use old magic to communicate with long - lost magical creatures that hold secrets of the wizarding world.
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.
Yes, it can be considered dark and controversial. Blood magic in the Harry Potter universe is often associated with dark and unethical practices. It goes against the principles of the good magic that Hogwarts teaches. For example, the use of blood in dark spells is seen in the actions of Voldemort. In fanfiction, having Harry Potter learn blood magic is a deviation from his character's usual moral stance, which can stir up a lot of debate among fans.
He could lose his friends. In the original story, his friends stand for good and oppose black magic. If Harry starts learning it, they might turn their backs on him. Also, he could be ostracized by the wizarding community. The wizarding world has a clear stance against black magic, and Harry would become an outcast.
One common theme is self - discovery. As Harry learns light magic, he often discovers new aspects of himself and his potential. Another theme is the power of good over evil. Light magic is usually depicted as a force for good, so it's about using it to combat the dark forces in the wizarding world.
In some fanfictions, Harry might learn family magic that has to do with time manipulation. His family could have had a special talent for seeing into the past or future. As he delves into this magic, he has to learn to control it carefully, as misusing time - related magic can have serious consequences. He may use this new - found magic to prevent certain disasters or to gain knowledge from the past that could change the course of the wizarding world.
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.
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.
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.