Kasane Kujiragi

Kasane Kujiragi (鯨木かさね, Kujiragi Kasane) is a wielder of Saika. Although mentioned in passing in previous volumes, she first appears in person in volume 10 as Jinnai Yodogiri's secretary and apparent niece and is later revealed to be the ringleader behind the organization that collectively operates under Yodogiri's name, thus making her the main antagonist of Durarara!!x2.

Appearance
Kujiragi is a young woman with long brown hair pulled up into a ponytail secured with a red bow. She wears glasses and a yellow skirt suit over a blouse and stockings along with Mary Jane pumps. She carries a large shoulder bag, and her brown eyes become red when wielding Saika.

Personality
Kujiragi is shown to be a very quiet and composed individual who rarely shows emotion. Despite her manipulation skills, she is a terrible liar when doing so face to face. As a wielder of Saika, she is also very skilled in swordplay and is capable of enslaving anyone she cuts like Anri and Haruna. She also uses a different method of enslaving others which she refers to as "Branching." This method involves smelting knives and other bladed instruments with fragments of Saika's blade mixed in.

Background
Kujiragi was born to the same family as Ruri Hijiribe and is the half-sister of Ruri's mother. However, she was sold to the original Jinnai Yodogiri in order to pay off some sort of debt her family owed. As such, she was raised by him through all of her life until Yodogiri eventually passed away. After this, she took on his identity and continued his work as an info broker but used 20-30 year old men as scapegoats while she played the role of the secretary. At some point, she acquired Saika, split it in half, and sold one half to Shingen Kishitani while keeping the other half for herself.

Kadota's Coma Arc
Kujiragi shows up first with Yodogiri when dealing with Shijima's family.

She talks to Nakura about Izaya and confesses to him that she isn't an insurance agent. She then appears with Seitarou Yagiri to kidnap his niece, Namie. Kujiragi incapacitates Namie by electrocuting her with an electric glove, which Namie remembers Izaya buying before for fun. Namie fights until they tell her they have her brother Seiji, at which point she makes interesting and terrifying threats to be carried out if they touch a hair on his head.

She makes a major appearance in the second half, where Izaya Orihara arranges for Haruna Niekawa's "children" to kill "Jinnai Yodogiri" by running them over. It is at this point that Jinnai Yodogiri is actually the name of a group as opposed to one man. When the Yodogiri ("Number Eight") beside her is injured, Kujiragi does not respond but proceeds to calmly call another Yodogiri ("Number Five"), with a similar voice, to replace him, only to hear him get knocked down as well over the phone. Izaya calls her, and confronts her as the leader of the organization "Jinnai Yodogiri." At this point, he is being guarded by Slon.

In the conversation, Izaya claims to have had no proof, only guessing based on his own research. On questioning, Kujiragi reveals that although "Kasane Kujiragi" is not her real name, the name was given willingly, and the original Kujiragi has likely started a new life in Southeast Asia. The men acting as "Jinnai Yodogiri" are said to have partaken willingly in the prior immoral actions in their own interest. Izaya says that Jinnai Yodogiri has been active since about twenty years ago, and asks about her age despite her young appearances. She claims to have no obligation to answer, evading the question. Izaya confronts her about spreading rumors in Dollars about Dragon Zombie, Izaya's hired bodyguards, having been the culprits behind Kadota's accident. He recognizes her impersonation of Kanra in the online chatroom as a warning and asks why she added "nya" behind her sentences. Kujiragi says that it's cute. Izaya is incredulous and asks if she wears cat ears and a tail in front of the mirror to pose and say "nya" on her days off. After silence, she says it sounds alright and she will try.

Izaya mocks her with the irony that Saika, which she sold to Shingen Kishitani, has become her enemy. He then video-chats Haruna with instructions to have Kujiragi kidnapped.

Kujiragi says that Izaya and Shizuo are obstacles for her motive of "bringing in goods," and reveals that she is aware that Izaya had Shizuo arrested. She proceeds to say that the "children" cannot focus with someone like Shizuo on the streets, although Haruna's "children" appear to have given up. She reveals that she was the owner of Saika twenty years ago. Izaya asks if being a previous owner has granted her some privilege, to which she replies that other than cutting, there is another method to increase Saika's children that the current wielders are likely unaware of. She calls this technique branching - to break Saika's original form, and use the shard to smelt another blade.

Izaya turns around, alarmed, only to be grabbed by the throat by Slon and smashed into the concrete. Kujiragi asks for Izaya to be taken to an office so she can question him regarding Celty's head.

After this, as she talks to herself, Kujiragi thanks Izaya for dealing with Jinnai Yodogiri and "freeing" her from her monotonous everyday life. She says Izaya is indeed an obstacle in Ikebukuro, third after the Awakusu organization and Shinichi Tsukumoya.

Saving Izaya/Haruna is back Arc
Shinichi comments on Kujiragi in a blog post. It is revealed that Kujiragi is a dhampyr, explaining her youthful appearance. It is also revealed that Kujiragi shares the same non-human mother as Ruri Hijiribe's mother, (although their fathers are a generation apart), resulting in Ruri being Kujiragi's niece with an age gap of about twenty years. Kujiragi was sold to Jinnai Yodogiri by her mother (Ruri's grandmother) shortly after her birth, about right after Ruri's grandmother ran out on the family. Having grown up under Jinnai Yodogiri's shadow, she continued using his name after he passed away. Shinichi compares her to Izaya, saying that if Izaya is naturally evil, Kujiragi is an evil made by humans, and thus a perpetrator as well as a victim. Having grown up in such a setting, Kujiragi's fate was mapped out from the start, and the only path of living for her now is the underground practice.

Supposedly, the Saika "branching" Kujiragi spoke of was when she sold Saika to Shingen. This means that two Saika blades already existed twenty years ago. Of these two, one is still in the possession of Kujiragi, whereas the other is with Anri Sonohara.

She is with Seitarou near a van with Namie beaten up in it. Then a man who looks like Shingen jumps in there and attacks her and Seitarou. Then two more Shingens appear and the real Shingen tells them about him having allies that look like him. While the allies are saving Namie, Kujiragi was asked a question from Shingen. The question was if she believed how human beings are not slaves. She doesn't give him a good answer.

She attempts to buy Saika from Anri but fails. Erika later convinces her to cosplay.

Final Curtain Arc
She meets Celty and Shinra. She kisses Shinra in front of Celty and stabs him with Saika, making him a child of Saika and kidnaps him. She traps Celty's shadow form with Saika, until Shizuo intervenes. She and Vorona fight Mikage to get to Shizuo and Izaya. When Shingen informs the three that Shizuo and Izaya had relocated, they stop their fight. Kujiragi leaves and encounters Shinra, who had managed to overcome Saika's curse, on a bridge. Under Shinra's request she loans her Saika to him. Later that same night, she saves Ruri from Adabashi and takes full blame for her crimes to spite her, jealous of how she is able to live her life normally.

Durarara!! SH
She is mentioned to have become a business associate of Anri's after she re-opened her family's store. She periodically visits Sonohara Hall for business and hangs out with Erika for their cosplay meetups. On one of her visits, she encounters Celty and asks how Shinra has been doing. Celty lashes out for her antics, but before the confrontation escalated too far, she proposes they move to a more remote area to talk. Once they do, Kujiragi answers her questions and in the conversation Celty brings up Bannanjin. Kujiragi informs her she left the cursed weapon in the Sonohara Hall's warehouse secretly, aware Anri would not accept it upfront, as an apology for the trouble Saika had caused from before and explains how Bannanjin functions in contrast to Saika.

Ruri Hijiribe
Kujiragi is envious of Ruri for chasing her own dreams and happiness despite having the same non-human blood as she. Kugiragi's envy, however, does not reach the point of hatred.

Shinra Kishitani
Kujiragi becomes interested in Shinra because of his purported love of Celty, a being she considers an aberration. She is skeptical of the claim, but her own digging into the matter reveals the truth, and she develops an unrequited crush on Shinra, hoping he could love a monster like herself, too. She is amazed by his willpower and ability to break the Saika curse she put on him, but he reminds her that she would never have fallen for him if he had not loved Celty first.

Trivia

 * Kasane's surname Kujiragi means "whale" (鯨, kujira) and "tree, wood" (木, ki/gi).