Well, the Basilisk could be a familiar given to Harry by a mysterious ancient magic. Harry initially struggles to control it as it has a very strong and wild nature. But as he spends time with it, he learns to communicate better. The plot could involve them going on adventures together, like exploring lost magical ruins. The Basilisk's ability to petrify could come in handy when they encounter dangerous dark magic traps or enemies. Harry has to constantly balance keeping the Basilisk a secret and using its powers for good.
One possible story could be about a dark wizard who manages to tame a basilisk as a familiar. The basilisk might be used to guard his lair and terrify any intruders. It could have unique markings or abilities that set it apart from normal basilisks in the original 'Harry Potter' lore.
A plot could revolve around a hidden prophecy that links the Basilisk and the Patronus. A young witch or wizard discovers this prophecy and realizes that they are the key to either saving or destroying the wizarding world. They must then navigate the dangerous relationship between the two magical entities. This could involve traveling back in time to learn about the origins of the Basilisk and the true nature of the Patronus magic, which could be much deeper and more complex than what was taught at Hogwarts.
In a fanfiction, the Phoenix and the Basilisk could be two parts of an ancient prophecy. Harry Potter is the one foretold to either unite them or destroy one to save the other. Along the way, he has to learn about the true nature of both creatures. He might find that the Basilisk isn't as purely evil as it seems and the Phoenix has a more complex role than just being a symbol of good. This could lead to a very engaging story full of moral dilemmas and exciting magical encounters.
A great plot for fanfiction could be a time - travel story. A wizard travels back in time to the era when the basilisk was first created or brought to Hogwarts. With the help of a special wand, they try to change the course of history regarding the basilisk. But every change they make has unforeseen consequences. For example, they might prevent the basilisk from being killed in the past, which then creates a new and more dangerous threat in the present. So, they have to find a way to fix what they've messed up while still dealing with the power of the basilisk and the wand.
One idea could be that Harry's lack of emotions makes him an enigma at Hogwarts. His friends are constantly trying to figure out what's wrong with him. Another could be that in the face of danger, like when facing Voldemort, his lack of fear or any emotion confounds his enemies. Maybe he can use this to his advantage in battles, making unpredictable moves.
One plotline could be that the Basilisk eyes make Harry a target for dark wizards who want to harness his power. He has to constantly be on the run and protect himself while also trying to figure out how to control his new ability. His friends from Hogwarts could form a sort of protection squad around him, and they'd have to face many challenges together.
One plot idea could be that the male basilisk is actually a cursed wizard who can only take the form of a basilisk. Harry discovers this and tries to find a way to break the curse. Another could be that the basilisk has a special power that can help Harry in his fight against Voldemort, so they form an alliance.
One idea could be a story where a young wizard discovers a chimera familiar that has unique powers. For example, it can fly faster than a hippogriff and has the ability to breathe fire and ice simultaneously. The wizard then has to keep this a secret from the Ministry of Magic as chimeras are considered dangerous and illegal as familiars.
One idea could be exploring the familiar's backstory. For example, if Harry's owl, Hedwig, was actually a descendant of a magical owl family with a special mission. Maybe it was sent to protect Harry not just as a normal owl but with some hidden powers or knowledge.
One plot idea could be that Harry's sister is secretly a powerful witch with unique abilities. For example, she might have the power to communicate with magical creatures in a way no one else can. This could lead to her getting involved in a plot to save a rare and endangered magical creature that is being hunted by dark wizards. Another idea is that she discovers a hidden prophecy related to her and Harry that changes the course of their fight against Voldemort. She could be the key to a new spell or magic that can defeat Voldemort once and for all.