The day to fight for Hogwarts dawned and found Hermione, Ginny and Luna preparing their hair for the battle. Rather than simply tying it up as they usually did in times when hair that long became even more impractical than it was most of the time, they were placing enchantments on it.
After not too long, Ginny's long plait, rather than falling to stop just before the floor, was up in the air, like a whip. This whip may or may not have been filled with sharp implements that Ginny had carefully planted to avoid them catching her. Hermione's wild hair reached out in long tendrils, giving her a Medusa-like appearance. Although hair may not appear like much, the thickness of Hermione's meant that a punch from one of those tendrils would be as hard as one from her fist. Luna's hair trailed behind her as a tail. A tail that could bring a man down with a sharp tug to the ankle.
Their hair also almost became sentient creatures. As easily as the hair waged war on the Deatheaters that filled the castle, not a single student was harmed by it.