Well, it could be a magical sword like the Sword of Gryffindor. In many fanfics, authors might choose this iconic sword as it has a strong connection to Harry through Gryffindor. It's a powerful weapon against dark magic and has a lot of history within the Harry Potter universe.
Well, it could potentially give him an edge in combat. Maybe he can use it to defeat dark creatures more easily. For example, if he faces a Dementor, the sword might be able to disrupt its form in a way normal spells can't.
The sword might be a gift from a mysterious magical being. This being saw potential in Harry Potter and decided to give him the sword as a tool to help him in his future battles. It could have been enchanted specifically for Harry to face the unique challenges he will encounter.
The sword could attract dark forces. Since it's a powerful weapon, it might act like a magnet for dark wizards or evil creatures. Harry then has to constantly defend himself and the sword from these threats, which can be really difficult especially if he's not fully trained in sword combat.
Maybe Firenze the centaur. Centaurs are known for their combat skills and Firenze, being friendly towards Harry, could teach him the art of sword - fighting. He might have a different perspective on combat compared to human wizards.
One fanfic that might fit this is 'The Female Harry's Adventure with the Sword'. In it, the female Harry Potter discovers an ancient sword and uses it to face new and unique challenges in the wizarding world. It's a really interesting take on the character and the addition of the sword brings a fresh element to the story.
In some fanfics, the sword is enchanted and has a mind of its own. The female Harry Potter has to form a bond with the sword, almost like it's a living being. This leads to some really interesting character development as she learns to communicate with the sword and use its powers to her advantage. She might have to face her own insecurities and fears as she does this. Also, the sword could be a symbol of a new era in the wizarding world, and her using it could spark a revolution or change in how magic is perceived and used.
One interesting plotline could be that the sword gives Harry Potter some special powers. For example, it might be able to cut through magical barriers that no other weapon can. This would make him more powerful in battles against dark wizards. Another plotline could be that the sword has a mind of its own and guides Harry Potter to hidden secrets or lost magical artifacts. It could lead him on a grand adventure where he discovers things about the wizarding world that were previously unknown.
Basilisk blood could potentially be used for healing in fanfic, but with great risk. It's so potent that it might be able to cure otherwise incurable diseases or wounds in a wizarding world, but its dark and dangerous nature could also have unforeseen side effects, like corrupting the user's magic or mind. For example, a character desperate to save a loved one might use it, only to find themselves slowly losing control of their powers.