Kaoru Nagumo (ナグモカオル Nagumo Kaoru) is introduced as a lovely young woman whom Chizuru Yukimura and the Shinsengumi rescue from thugs in the street. It is later revealed that Kaoru is really a young man and Chizuru's twin brother.
Kaoru has his own reasons to hate Chizuru and wish her suffering which is why he is involved into multiple situations that are meant to hurt his sister.
Appearance
The Shinsengumi members notice that Chizuru looks almost exactly like Kaoru as they are twins, except for the fact that they wear different clothes. They both have long brown hair and light-brown eyes, and Kaoru's facial features are quite feminine despite him being a boy.
In his disguise form, Kaoru takes on a female appearance, tricking those who do not know him by wearing make-up, accessories and a female kimono of pink color. He also acts like a gentle woman at this time.
When Kaoru drops his disguise, he cuts his hair and puts on male dark-blue clothing with a black cape on top of it. He also wears his family heirloom (katana) on the left side.
Past
This article contains major SPOILERS. Be careful if you do not know the full story yet.
Kaoru was born into the Yukimura Clan, a demon clan residing in the East of Japan. After humans had tried to destroy the Clan, he escaped with his life along with his twin sister, Chizuru. Being caught by the government as the few remaining survivors of the Yukimura Clan, Koudou was forced to give Kaoru to the Nagumo family.
During this time, he had suffered emotionally and physically because he was not a female demon. Hearing that his sister was living a much better life than he did, he wished for his sister's despair.
It is also known that he was given the Yukimura Clan's heirloom, the katana, so it should be assumed that he was taught to use it from the Nagumo family who took him in.
Story
First Season
Chizuru first meets Kaoru as a woman on the streets by chance when Okita, Heisuke and others save him from thugs. Okita instantly notices the incredible resemblance between Kaoru and Chizuru, but Heisuke denies that. Kaoru promises to thank Okita one day.
Later on, Harada is protecting a noticeboard when a group of rebels attacks his unit. He almost wins when Kaoru appears and kills some of the Shinsengumi members while freeing his own men. Harada is shocked, mistaking Kaoru for Chizuru which apparently was Kaoru's agenda.
Throughout the first season, Kaoru is seen spying on the Shinsengumi and especially Okita, seemingly enjoying Souji's progressing tuberculosis.
When Okita becomes too weak and unable to stand, Kaoru appears and gives him Ochimizu that is promised to cure him. However, when he later attacks Kaoru, it is revealed that Kaoru lied, and Ochimizu cannot cure tuberculosis. Kaoru also tells Souji that he is Chizuru's older twin brother, and that the two were separated at a very young age. Kaoru wishes to make Chizuru suffer, since he himself was treated very badly by the demon family that took him in, just because he was not female. He shows a very vicious personality when he admits that he was the one who advised Itou's followers to lay down near the road that Kondou would use so that they could shoot him. He also sets a trap for Chizuru and Heisuke who run after Souji (people with guns lurking in the shadows), and when Souji notices that and protects his friends, Kaoru smiles and says that Chizuru will suffer even more.
Second Season
Kaoru is shown to work with Koudou Yukimura and inform him of the Shinsengumi's movements.
While Chizuru and Kondou are on their way to Edo, Kaoru stops them and demands Chizuru to join him. He reveals being her older brother and that Koudou is not their actual father but rather a distant relative from another branch. To prove his words, he shows Chizuru his sword that is meant to be paired with hers as a Yukimura clan heirloom that has been passed down through generations. When Chizuru refuses to follow him, he claims that Koudou has created a new kind of Rasetsu, so Chizuru's friends are most likely dead. Kondou rushes to attack him but fails, and Kaoru uses it as a reason to say 'I am the only one who can protect you'. Chizuru decides to fight him, but he defeats her quickly. Okita joins the scene but fails due to his tuberculosis. By the time Kaoru is ready to do the final blow, Kazama pierces through his heart and kills him.
Even though Kaoru cries and claims to love Chizuru while asking her to join him and restore the Yukimura's glory, it stays unclear whether he actually means it since his final words are 'why is it always you?' which refers to the fact that female demons are more precious, and Kaoru, as a male, was jealous of Chizuru's gender wishing her to suffer as much as he did. Another proof of his impure intentions is the fact that he is about to kill Chizuru right before Okita comes for rescue.
Sweet School Life
In the short OVA Kaoru is a First Year Form Two (1-2) student who is part of the Discipline Committee at Hakuo Academy. He takes his job seriously and attempts to uphold the rules stopping Heisuke, Okita and Chizuru from entering the school gates as they are late for the class. He is protective of his sister and gets annoyed when she is involved with any men whatsoever (for example, when she starts blushing seeing a lot of half-naked men in the gym, he asks whether her red cheeks have anything to do with her liking someone in particular).
Trivia
- Kaoru means "fragrance" and Nagumo means "southern cloud" in Japanese.
- Kaoru is Chizuru's twin brother who was separated at birth. He wants Chizuru to suffer, since no one ever protected him.