Head plates were invented by an old forgotten clan that was obsessed with luck. Before battle they used prophets and shamans to predict where on their head the next fatal blow was due to land, then position the metal plate on their head accordingly. Sometimes it worked, sometimes it didn't. Such is luck, they would say.
Hachigane is armor that is equipped in the head slot. It belongs to the Light Armour Class and can be crafted using the Heavy Armour Smithy.