Nagi Kirima (霧間 凪, Kirima Nagi) is the deuteragonist of the Boogiepop Series, as well as the protagonist of the Repent Walpurgis Series. Known and feared around her school as the dangerous Fire Witch (炎の魔女, Honō no Majo), she is the daughter of the famous and enigmatic writer Seiichi Kirima, the non-blood-related sister of Masaki Taniguchi, and a friend of Naoko Kamikishiro and Kazuko Suema.
Unbeknownst to even herself, she is the vessel of the Witch of Fire, Walpurgis (ヴァルプルギス, Barupurugizu), mortal enemy of the Witch of Ice, Alcestis. Her ability almost killed her when she was young, but it was supressed with the help of Shinpei Kuroda.
Nagi is a tall and imposing young girl with long brown hair and brown eyes. While at school she wears the Shinyo Academy white female sailor uniform, but while on her missions, she wears a black leather skin-tight suit, black gloves and black combat boots.
As Walpurgis, Nagi's hair grows significantly in length, and becomes white, and her skin becomes red, and is covered with several black lines. In this form, the top of her leather suit is unzipped, showing her cleavage, and her gloves, as well as a portion of her suit's sleeves are torn off.
In the anime, Nagi has shorter, shoulder-length black hair, and is seen wearing the Shinyo Academy school uniform, consisting of a blue blazer worn over a white shirt with a red tie around the collar, and a pale blue short skirt, as well as her black skin-tight suit, black fingerless gloves and black combat boots.
Infamous around school for her delinquent behavior, Nagi is an aggressive and brutish individual, unconcerned with any of the Academy's regulations. The teachers cannot find ways to admonish the girl, as she always gets top test scores, and no matter how much she skips school, always knows the subjects taught perfectly. Her threatening demeanor, however, is in fact just a ruse, in order to keep average people away from her. According to herself, after witnessing her father's death, Nagi developed a serious messiah complex, always wanting to "save the day". Her intense wish to become a savior has led her to always get involved any time an enemy of the world rises up. Because of this, Nagi keeps running into Boogiepop and, as the two have the same goals, they developed a collaborative relationship, although Nagi doesn't seem to hold him in very high regard.
She has a relatively good relationship with her brother Masaki, caring after him and doing her best to keep him out of any trouble. Her only friend for most of her time at Shinyo Academy was Naoko Kamikishiro, who she really cared for, starting her hunt for the Manticore because Naoko asked her to help Echoes. Later, however, she also developed a friendship with Kazuko Suema because of the girl's constant insistance, as well as with Kei Niitoki, after their battle with the Manticore. She also became good friends with Kentarou Habara after saving him, and with Aya Orihata, naturally interacting with her after she became her brother's girlfriend.
After Naoko's death, Nagi started to keep all of her friends away from her missions, as she didn't want any more of them to suffer. Kentarou, however, still always tries to insert himself into her business, wanting to prove himself to her. Nagi uses male first person pronouns, and generally speaks in a very boyish manner. It seems she has had this way of speaking ever since she was young, as she was already like this by the time she met Shinpei Kuroda. She dislikes her name, because everyone she meets always misreads it.
Nagi was the daughter of Kyouko Kirima and Seiichi Kirima. Though, not known by either Seiichi or Nagi, Kyouko was actually the former vessel of the Witch of Fire, Walpurgis, and has lived for hundreds of years. When she birthed Nagi, she transmitted Walpurgis from herself to her child.
Seiichi was a famous writer, who Nagi idolized a lot, so much so that she admitted to Kazuko that she had a father complex. However, not long after her birth, Kyouko divorced Seiichi, and, not being able to afford taking care of Nagi, left her with Seiichi. She then soon met and married Shigeki Taniguchi, who already had a son named Masaki Taniguchi. Since Shigeki was a very wealthy man, Kyouko invited Nagi to live with them, but she refused, opting to stay with her father.
Unfortunately however, she wittnessed her father die in front of her when she returned home. The man suffered a gastric perforation which, according to Nagi, was a terrible way to die, although the true cause of his death was the assassin Mo Murder, sent by the Towa Organization. Afterwards, she became the Taniguchi family's child on paper, but kept Seiichi's surname, as a sign of respect for him.
During elementary-school, Nagi studied at the same school as Kasumi Mikage.
During her time in middle-school, Nagi befriended Naoko Kamikishiro. Later, the girl started going through serious bouts of pain, which she described as unbearable. She was admitted to the hospital, with doctor Makiko Kisugi looking over her, who brushed off her sessions of pain as just a particularly severe case of growing pains. However, Shinpei Kuroda figured out that she was actually a case of an incomplete MLPS, whose evolution failed. As a Towa agent, it should have been Kuroda's duty to give her to the Organization, who would conduct countless experiments on her before disposing of her. Kuroda, however, was compelled to save the girl, and so he stole a drug that would remedy the effects of her failed MPLS abilities, and turn her into a normal human again, thereby betraying his employers, and getting himself killed.
When Nagi asked Kuroda what she should become, the man answered that the best thing to be would be a superhero, which inspired Nagi to start her clandestine activities and try to settle all the situations she came across. A few years after the start of her heroic career, Nagi saved Kentarou Habara, who was close to being arrested for his hacking escapades. After that, Kentarou became an ally of Nagi's, who would help her whenever given the chance.
- Repulsion (斥力, Sekiryoku): The main ability of the Witch of Fire, Walpurgis. It is the ultimate repulsive force that can blow away anything. It used to possess energy that exceeded human understanding, but has since weakened, and is now equal to the ability of Alcestis, although completely opposite to it. Aside from Repulsion, Walpurgis possesses the same mind-boggling abilities as the other Witch, including time manipulation, interference with parallel worlds, traveling between universes, reading the minds of every living being on Earth, tearing apart the fabric of the universe, interference with the soul and manipulation of fate.
- The name Nagi means "calm, lull" (凪), which is something that Seiichi Kirima gave it to her because he wanted her to always be calm, no matter the situation.
- Nagi's surname Kirima means "fog, mist" (霧) (kiri) and "time, while, interval, space" (間) (ma).
- The nickname "Fire Witch" is a reference to the song "In The Court Of The Crimson King" by King Crimson, specifically to the lyric "To summon back the Fire Witch, to the court of the Crimson King".
- The name of the Witch of Fire, and the name of Nagi's spin-off series, are both references to the song "Repent Walpurgis" by the band Procol Harum.