Mu-12/Biography

Continuum Shift
"The Successor of the Azure and the 12th Prime Field Device, as well as the true form of Noel Vermillion. The sublimation of the Murakumo Unit, the "Sword of the Godslayer Kusanagi" shown itself for the sake of destroying the "Master Unit Amaterasu"..."

Chrono Phantasma
"The Successor of the true Azure and the awakened form of Noel. The ultimate Boundary Interface Prime Field Device. She was the "Sword of the Godslayer Kusanagi," the only one able to destroy the Master Unit that exists in the Boundary, but with the help of Ragna, Noel was able to retain her self-identity. So, to save her best friend, she asks Rachel to teach her how to control this power."

When Noel created the Realm, an imaginary space out of her own subconscious, Rachel helped the girl try to accept herself. This led to Noel coming face-to-face with a reflection of her soul that she did not want to initially accept or even acknowledge – Mu. Noel won her battle and, with Rachel's encouragement, accepted her power, gaining access to Mu's form. This was tested against Nu-13 shortly afterwards, leading to the first known clash between two wielders of the Lux Sanctus: Murakumo. The Realm collapsed shortly afterwards, but Mu's power was now accessible by Noel.

Noel activated Murakumo again, relying on Mu's power to help her battle against Ragna as he was sent berserk by Izanami. She failed to stop him and he disappeared after gravely injuring Jin.

Central Fiction
"The Successor of the Azure and the 12th Prime Field Device, as well as the true form of Noel Vermillion. She awoke in Kagutsuchi as the "enemy of the world," and was attacked by her friends one after the other. In order to discover the true meaning behind this phenomenon, she begins to act."

During the confrontation with Ragna, Mu was split from Noel's soul and became her own separate entity, but maintained Noel's memories and personality. Mu-12 was also absorbed into the Embryo, but was sent to a different world from the others. In this reality, she had murdered many people, including her friends. She discovered Makoto while still unaware of her circumstances and was attacked by her. She fought back and knocked her former friend down.

Inside the NOL branch of Kagutsuchi, she found Tsubaki, who turned her blade against the Godslayer and asked if it was fun to kill so many people and take their futures away from them. Tsubaki transformed into Izayoi, and the pair fought until a phenomenon intervention took Izayoi away. Mu began to despair over her circumstances, but resolved to find the Cauldron. Kagura blocked her way, his words making her lose control. She fell into a depression and stopped acting like Noel and more like the original Mu-12. Once she killed the illusion of Kagura, the cauldron opened itself up.

Inside the cauldron, Mu discovered Es guarding the Forbidden Gate -Altar-. The two fought briefly before Mu lost to Es, and was sent back to the original, real world. There, the real Hazama found her and managed to manipulate her into a robotic trance, whereupon he ordered her to kill the real Ragna. She complied, but Ragna freed her from her trance, and she was able to direct him out of the phenomenon event and back to his original reality. Mu attempted to follow but couldn't, and asked Ragna to bring Noel to a cauldron so she could fuse with her again. Ragna fulfilled his promise and brought Noel to a cauldron, but Noel rejected Mu, forcing Mu to wait until her other half was able to accept her.

Mu was finally accepted by Noel later when the latter used the Azure Grimoire as a cauldron. With this, Mu finally reunited with the other half of her soul. Noel would later use Mu's power to fully absorb Izanami and Saya into herself, and become the complete whole of Saya.