A wizard who was once a victim of the basilisk's petrification but managed to survive in a half - petrified state and has unique knowledge about the basilisk's lair and weaknesses. He might be an outcast in the wizarding world because of his condition but becomes an important ally in the fanfiction.
There could be a young witch from a far - off land who has a special ability to communicate with snakes, even better than Slytherin himself. She could be added to the story to either help or hinder Harry and his friends in their battle against the basilisk.
An old caretaker of Hogwarts who has been secretly protecting the basilisk all along because he believes it is a misunderstood creature. He has a deep connection with the Chamber of Secrets and his backstory could be explored, adding more depth to the fanfiction's plot.
Obviously, Harry Potter himself is usually one of the main characters. He is often the one who has to face the basilisk in these fanfictions.
One original character could be a wizard named Aiden. He has the power of teleportation but can only do it within a certain radius. This limitation makes his power both useful and challenging. There could also be a witch named Celeste who has the power of charm - speaking, which is like a super - powered version of the Imperius Curse. She can make people do almost anything she wants just by speaking to them in a certain way. And a centaur named Brutus who has the power to read minds at a short distance could be added. He could be an ally or a source of information for Harry and his friends in the fanfiction.
A young witch named Luna, not the same as Luna Lovegood, who has the power to control the weather within the Hogwarts grounds. She could be a new friend for Harry and get involved in his adventures. Another could be a wizard named Orion, who is an expert in ancient runes and helps Harry decipher some hidden messages. There could also be a half - elf named Elara, who works in the Hogwarts kitchen and has a special connection with the magical plants there.
An interesting original character could be a half - elf named Elio. He works in a Diagon Alley bakery, baking magical pastries with ingredients that have special properties. He has a troubled past, being half - elf, and is trying to make a name for himself in the wizarding world. Also, a character like a young wizard named Finn who is a bit of a troublemaker. He's always getting into scrapes in Diagon Alley, whether it's accidentally setting off fireworks in the middle of the street or trying to steal a peek at the new brooms in Quality Quidditch Supplies before they're officially released. There could also be an old wizard named Aldric who has a shop full of enchanted maps that show not only the wizarding world but also hidden realms that no one else knows about.
A young half - elf who becomes Harry's secret helper. This character could have unique magic abilities that are a blend of elf and human magic. Another could be a wizard from a far - off land who comes to Hogwarts as an exchange student when Harry is a hatchling. He might bring new spells and a different perspective on magic.
Some fanfics introduce a new magical creature as a character. For example, a sentient phoenix that can communicate and has its own motives during the events of the Goblet of Fire. It could befriend Harry and help him in ways that Dumbledore's phoenix, Fawkes, couldn't.
Harry Potter is the central figure for sure. His friends, Ron and Hermione, are likely to be important as they usually are in Harry Potter stories. In addition, there could be antagonists who are either against Harry because of his strange origin or are trying to use his basilisk - related powers for their own evil purposes. There might also be some sort of basilisk - like creatures or characters with a connection to basilisks that play a significant role in the story.
Fanfictions often change the way the Basilisk is defeated. Instead of the traditional way in the books, the characters might use different strategies or magical items. Also, the relationship between the Basilisk and other characters can be completely different. Maybe the Basilisk teams up with a character against a common enemy in the fanfiction world. This is a big deviation from the original where it was a clear antagonist.
A half - veela character who uses her charm to get ahead in the Ministry but then realizes the importance of true merit. She could add an interesting dynamic to the often - stuffy Ministry environment.
In many fanfictions, Severus Snape could be involved. He has a deep knowledge of dark magic, so he might be either trying to prevent the basilisk ritual from being misused or he could be lured by the power it offers. Dumbledore is also a likely character. He would be the one to guide the students or other characters in dealing with the implications of the basilisk ritual. And of course, Tom Riddle (Voldemort) could be a key figure if the ritual has something to do with his rise to power or his plans for the wizarding world.