Kasane Kujiragi

Kujiragi Kasane (鯨木重) is a character in the Durarara!! light novel and a wielder of Saika. Although mentioned in passing in previous volumes, she first appears in person in Volume 10 as Yodogiri Jinnai's secretary, and is later revealed to be the ringleader behind the organization that collectively operates under Yodogiri's name.

Characteristics
She is described as being a young woman wearing a western suit (usually yellow). She is shown to wear spectacles in illustrations. She has has black hair, pale skin and red eyes when using Saika.

Kujiragi is shown to be a very quiet and composed individual and rarely shows emotion. 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 her biological older sister. However, she was sold to the original Yodogiri Jinnai 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 others as scapegoats while she played the role of the secretary.

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

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 "Yodogiri Jinnai" by driving them over. It is at this point that Yodogiri Jinnai 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 "Yodogiri Jinnai". At this point, he is being guarded by Sloan.

In the conversation, Izaya claims to have had no proof, only guessing based on his own research. On questioning, Kujiragi reveals that although "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 "Yodogiri Jinnai" are said to have partaken willingly in the prior immoral actions in their own interest. Izaya says that Yodogiri Jinnai 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 body guards, 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. (Niekawa Haruna's Saika's children attacked Yodogiri Jinnai.) He skypes to Niekawa 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 Sloan 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 Yodogiri Jinnai and "freeing" her  from her monotonous everyday life. She says Izaya is indeed an obstacle in Ikebukuro, third after the Awakusu organization and Tsukumoya Shinichi.

Saving Izaya/Haruna is back Arc
Tsukumoya Shinichi comments on Kujiragi in a blog post. It is revealed that Kujiragi is a halfbreed, 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 Yodogiri Jinnai, 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 Yodogiri Jinnai's shadow, she continued using his name after he passed away. Tsukumoya Shinichi compares her to Izaya, saying that if Izaya is naturally evil, Kujiragi is a human 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.

Being that Ruri Hijiribe, despite having the same non-human blood, has managed to chase her own dreams and happiness, it is mentioned that Kujiragi does feel somewhat envious, but not to the point of hatred. For example, when Hijiribe met misfortune, it is said that Kujiragi did not feel satisfaction from it.

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 a good answer to him.