A quiet yet angry sword woman searching for the assassin who killed her family.
In the prelude manga, Naoto watched her parents shield her with their bodies as a person with a sword cut through them so hard and so fast that the sword managed to cut through both of them and left a large scar across her torso as she nearly died with them. A man called Fuyumine later came and offered to save her, but she wasn't in a position to refuse, so he sheltered her and helped heal her wounds. Naoto didn't have a name, so the man called her Naoto and that name stuck. The man decided to train her how to fight so she could survive on her own, and how to really use her hate. He wanted her to hate him, to want to kill him, because that was supposed to give a meaning to her life. Naoto didn't remember anything about her parents or the one who killed them, but learned how to fight so one day she could find that person.
Naoto got a job to deliver jornal around town and one day when she got home, Naoto saw that one the man's former students, Magato, had killed Fuyumine. In a rage, Naoto engaged Magato in a swordfight. Naoto was still learning how to really fight, but suddenly she felt like her body was moving on it's own, faster and better. She reminded all that Fuyumine teached her, and cut Magato deeply. Magato revealed to her that her name was given after another "Naoto", the "Original Naoto".
Naoto took Fuyumine's sword, and wander on the streets, delivering newspaper and trying to collect information about the sword, the truth about Fuyumine and the entrance to the "Underground". One day after talking to a few guys (and almost killing them), she heard about "Haine Rammsteiner" and that he was also looking for the Underground. After finally finding him, she got to "Liza", an old woman with cat ears. Liza was scared when she saw teh blade that naoto was carrying, and explained that a while ago, some kind of army using exactly that same sword was walking on the streets kidnapping kids and murdering whoever tried to stop them. But one man, Fuyumine, suddenly started to "rescuing" some of the kids, and also carrying the same sword.
Relieved that Fuyumine wasn't a murderer or a bad man after all, she decided to follow Haine and look for the real erson who murderer her parents. She is really protective with Nill, and even after a "bad start" with Haine, she kinda understands him and started to get along with him.