Nagisa Sagan (目渚 Sagan Nagisa) is an easily angered woman who conducts experiments, and creates humans who cannot feel physical pain known as Zeros. It is later revealed that despite her young appearance, Nagisa is over 30 years old. Little is known about her background; It is known she had a sister, but what has become of her sister has not yet been confirmed. She created Youji Sagan in her younger sister's image, perhaps as an attempt of remembrance or to erase a pain in her heart, but reasons are still unknown. Her over-the-top behavior and strange lifestyle leaves her alone and alienated. She befriends 7, and shamefully confesses that she is her only friend.
Her relationship with Ritsu Minami is an intriguing one. She puts up a front of hating him deeply, and wishing for nothing more than to see him fail. However, there are small moments that reveal possibly deeper feelings, as she blushes deeply whenever he is near her or touches her, though she steadfastly denies caring for him. Starting in volume 3 and finishing in Volume 4, she makes a bet with Ritsu that her older Zero pair, Yamato Nakano and Kouya Sakagami, can beat Ritsu's former student Soubi Agatsuma. Ultimately Yamato and Kouya are defeated, and Nagisa's sibling rivalry-like attitude towards Ritsu continues.
- Nagisa was revealed as one of the seven members of Septimal Moon in the latest chapter of Zero-Sum Monthly Comic (March 2008), though both she and Ritsu Minami had previously denied any affiliation with the group.
- It is completely unknown where Nagisa has been receiving funding for the Zero project.
- It is somewhat difficult to fathom that someone as childish as Nagisa was capable of creating the Zero project.
- Nagisa's name may be a reference to the American scientist, Carl Sagan.
- 7 mentions that Nagisa had a sister complex