Natzumi is Mimi's younger sister. She is also one of the geishas serving under the daimyo, Itsuki Shinju.
Natzumi was the youngest of the Kuroshika siblings, because of that she was constantly protected by her elder siblings. She hated the fact that her entire family is underestimatieng her because of her birth order, and she was very rebellious. She was in good terms with her eldest sister, Mimi, though Mimi treated Natzumi the same way her other siblings treated her. Natzumi only saw her mother once, and then she never saw her again. Her father on the other hand, was killed in front of her very eyes along with her elder brothers. She hated the bandits who killed her parents, and she resolved to help anyone who fell victim to them. She and what's left of her family moved into a secluded place, Mimi married a local. When Mimi gave birth to four children, the bandits attacked them once again, this time they killed her remaining brothers. Because of this they moved once again, but this time more tragedy awaited them as the bandits killed her brother-in-law and two of her nephews. Natzumi was fascinated with Mimi, who was able to keep calm and collected amidst all the tragedy and insanity around them.
Soon, Natzumi saw the bandits burning down a small house. She rushed inside and saw the unconscious Matsuda Arashi, holding onto some swords. She took him out of the house along with the swords he was holding on to. She brought him to the house where her sister and her remainig sons were staying in. Natzumi tended to Arashi's wounds, knowing that Mimi is still in shock. When Arashi woke up, he asked her why she saved him, to which she jokingly replied that he was so young and still hasn't expereinced falling in love yet. Natzumi was completely oblivious of Arashi's feelings towards her, even when her sister supported Arashi.
Once when Natzumi was hiking with Arashi, she missed her step and almost died. But Arashi saved her from falling and ultimately dying. Arashi stated that it would be a shame if she dies. Natzumi clung to him and wailed, saying that she was afraid of dying and was afraid of blood. Arashi held her tightly and she continued crying.
She was surprised when Arashi gave her a black hair ornament, along with some promises that a normal man would never say to a woman he considers his friend. Natzumi asked why he was saying those things to her, to which Arashi replied that he was in love. Natzumi, due to her stupidity, minsuderstood and thought that Arashi was refering to someone else, therefore she encouraged him to tell her how she felt before he looses her.
The next day she saw the bandits who killed her family members. They chased her all the way to the doorway of their house. She knew that she could not let Mimi be endangered by them once again. She asked them what their intention was, to which they replied that they wanted to lure Arashi out to kill them. Natzumi resisted, but she didn't want Mimi or Arashi to find out. In the end she was knocked out unconscious by one of the bandits. When she awoke, she provoked all of the bandits to anger. One lost his patience and hit her head on a rock, but quickly patched it up afterwards. Despite the fact that she didn't want to be rescued, Arashi tacked them down and saw her in an injured state, causing him frenzy and resulting to the death of all the bandits present.
Natzumi awoke days after Arashi left for Kyoto. When she woke up however, she had amnesia. She completely forgot everything that happened in her life. Mimi decided not to remind her of her painful memories, so she kept quiet about it. Nonetheless, Natzumi's attitude, behavior, manners and her naive nature didn't change.
Soon however, the resources around them became scarce. Mimi and Natzumi had to save whatever they had to survive. Mimi refused to keep on living when her remaining children died from the cold. Natzumi insisted that they go to Kyoto with the money their father left them, but Mimi made up her mind. Natzumi, half-heartedly, left her sister and went to Kyoto.
Natzumi met Karakisawa Hanami when she got on the port of Kyoto. Due to their similar circumstances, they easily sympathized one another. Natzumi befriended Hanami, and they parted. Natzumi found herself helplessly lost, she had nowhere to go, she knew no one in the place. She was saved by Hanami and Omaru Aoi, who brought her to the western dojo of Itsuki Shinju, the current daimyo of Kyoto. There Natzumi found out that Aoi is actually an oiran, a geisha of the highest rank, and she was recruiting Hanami as a geisha in exchange for a place to stay. At first Natzumi was reluctant to accept the offer, but due to Hanami, Aoi and Miyamoto Haruka's persuasions, she yielded nonetheless. However, Natzumi wasn't really welcome among the other geishas. Even with the cold welcome from her, she strived to become a geisha under Aoi. She became friends with Mikenda Itsuru, Iruzawa Azune and Nokumada Ritsu.
During her training session with Aoi, she inquired out of curiosity as to why Aoi became a geisha. Aoi replied that she became a geisha out of her own free will. Aoi stated that she wanted to help her uncle (Shinju) to become a great daimyo, for that cause, she sacrificed everything she had. Natzumi asked if Aoi ever doubted what she did, to which Aoi replied that she had no right to doubt her actions because she wanted all of it to happen. Naztumi asked as to why Aoi decided to teach her, but Aoi didn't reply and told Natzumi to continue with her training.
After a few weeks, her training was finished, however the treatment of the geishas towards her and Hanami didn't change. She was supposed to be presented to Horodo Tatsumaki before she can join the mission of the geishas: to seduce the opposing daimyos and kill them in bed. But Natzumi said that Aoi forbade her to meet Tatsumaki unless she said so.