The Zero Project is an experiment that was launched by Septimal Moon member, Nagisa Sagan. The Zero Project was a secret experiment that was established with the goal of creating the ideal fighting pair. The Zeros were designed to fight opponents but, experience "zero" pain (fight to the death). This trait is what earned the Zeros their name.
Main Article: Zero (Female)
The 1st Generation consisted of two females, Kouya Sakagami and Yamato Nakano. The role of Sacrifice was taken on by Yamato and the role of Sentouki was taken on by Kouya. The 1st Generations served as a near perfect fighting pair after a series of trial and error. Despite being the 1st Generation, their level of intelligence and combat efficiency greatly surpasses that of their successors, seeing that they have more experice that the second generation. The most undeniable sign of the 1st Generation's superiority was proven when the pair performed a spell that was powerful enough to incapacitate the 2nd Generation's Sacrifice. However, it is unknown if the pairs efficiency was available upon their creation or if they improved over time. It can be noted that Kouya and Yamato's bond progressed over time to the point that they became lovers. This trait could have been one of the pairs flaws since their love for each other became strong enough to the point that they disobeyed Nagisa's orders and broke off all connections with her.
Main Article: Zero (Male)
The 2nd Generation consists of two males, Natsuo Sagan and Youji Sagan. The role of Sacrifice was taken on by Youji and the role of Sentouki was taken on by Natsuo. The 2nd Generations featured few changes both aesthetically and performance wise from their predecessors. The first and most obvious changes were age and gender. Unlike their predecessors, the 2nd Generations used any means necessary to fulfill their tasks using methods such as provocation and deceit. The pair also seem unyielding to pleas of mercy to the point that they would push their targets to the brink of death unless defeated or recalled by Nagisa. However, the 2nd Generations can be persuaded if one of the two members are injured or mortally ill. . Unlike their older counterparts, the Sagan brothers are blood related and hold a relationship that does not surpass brotherhood, although through the series, they often are seen flirting with Ritsuka, Youji kissed him and tried to undress him and Natsuo likes touching his ears. Or each other, always either holding hands or hugging in a non "brother" way. The 2nd Generation Zeros share the same last name as Nagisa. Youji was also designed to look identical to Nagisa's younger sister. For these reasons, Nagisa probably favored them over their predecessors.
Below is a list of ongoing flaws with Zero subjects:
- Inability to adjust to dramatic decreases in climate temperatures.
- Tendency to disobey orders.
- Entirely aware of their inability to feel pain.
- Tendency to question their existence.