A bloodsword is a type of Gem Sword that is rarely ever seen. It was originally part of the original Twelve Swords of Gondra, but was removed, because of the "blood-lust" it seemed to give it's wielder. It was replaced with the Aquasword. Only one family seems to have the only Bloodsword in existance and that's the Blackstar family. However, it's possible that there is more than one bloodsword in existance.
It also can blind someone if the light is reflected off of it the right way.