Nu-13 (Sword of Izanami), is a playable character and is one of the main antagonists in the BlazBlue series. She was thought to be a main antagonist as of the first game Calamity Trigger, until she is demoted as one of supporting antagonists after the first game. She returns as a playable character and as an antagonist in BlazBlue Cross Tag Battle.
Nu-13 is one of the so-named Prime Field Devices designed by Relius Clover for the purpose of exploring the strange dimension called Boundary and finding the Master Unit: Amaterasu. She's also the first successful Murakumo Unit, who's designed to be able to wield the Nox Nyctores Murakumo to be used as a combat unit. She normally acts as robotic as she appears, but she also for some reason has an unhealthy obsession with Ragna, towards whom she shows more of her human side - in a rather creepy way, which Ragna doesn't reciprocate.
Utilizing her Murakumo, she can attack by using a set of flying blades that she can manipulate in various ways, and her ability Sword Summoner lets her summon even more blades to impale her enemies from far away.