Halua, also known as No. 6, is the older sister of Emil.
At the National Weapons Laboratory where she and her brother resided as children, they were experimented on in order to make the ultimate weapon. Emil's mansion was used as a front, while there were secret underground labs under the building. After excessive experimenting, Halua was transformed into Number 6, a skeletal monster. However, because her human heart was still left intact even after the remodeling, she went berserk. Her powerful magic could not be controlled by the researchers, and she had to be chained and bolted to a wall to stop her destroying the mansion. Emil was remodeled into No. 7 to keep her in control. Emil and Nier, searching for a way to cure Kainé's petrification, find Number 6 in the underground labs. They fight No. 6, and she fuses together with Emil after their battle, granting him all her power and also transforming him into a skeletal creature.
- In the early development stages, there were plans of her being a party member instead of Emil.