Nu-13 is a Murakumo Unit who was sealed in the Sheol Gate. She is a playable character in BlazBlue: Calamity Trigger and reappears in the sequel, Continuum Shift as Lambda's Unlimited form. She was programmed to terminate anyone she deems as hostile subjects that came near the Gate. Nu-13 is also shown to have a split personality, split between an emotionless girl when around others and a yandere when around Ragna the Bloodedge, though this may be how she was programmed to act. Nu-13 wants to absorb Ragna and have him join her in destroying the world, because she, too, possesses a piece of the Azure Grimoire (although neither she nor Ragna realized the pieces they possess were actually imitations). When Ragna refuses to join her she decides to take him by force. She also knows Hakumen, recognizing him as a "Sankishin Unit".

She, as with Noel, was made as a replica of Saya, Ragna and Jin's sister. They seem to share some of Saya's memories, though nothing congruous. In the true ending, she tries to merge with Ragna by falling with him into the Cauldron. However, Noel thwarted her efforts and saved Ragna's life. Nu dies after falling back into the Cauldron, and failing to fuse with Ragna.

In BlazBlue: Continuum Shift, she is replaced by Lambda-11 of Sector Seven, however returns as Lambda's unlimited form in the console version of Blazblue: Continuum Shift. She, in Lambda's body, assists Tager on Kokonoe's orders though her memories are suppressed. Eventually Hazama coaxes her memories as Nu, causing complications in her programming. Under Phantom's influence, Lambda is forced into a battle against an illusion of Nu in her Story mode, becoming comatose if she loses.