Kaidou Shikiko is Kaidou Kio's daughter. She appears in chapters 81 and 82, in volume 10 of the Loveless manga. She hasn't reappeared nor have the mysteries of the Kaidou family been discussed since then. In the chapter, Kio returns to his family home for advice after he is kidnapped by Nisei and Seimei. While at the Kaidou home, Kio first speaks to Shikiko who is revealed to be his daughter, and then her mother, with whom Kio's relationship is unclear.
Notably, Shikiko does not have ears, making her an 'adult.' She also appears to be quite young. She is very close in age to Kio, her father. Shikiko is either the current head of the Kaidou household or future head of the household. This position was decided upon before her birth.
Shikiko has long hair that falls past her waist with a braid on the left side. She has long bangs and a flyaway hair that notably sticks up from the top of her hair.
She dresses in a very feminine dress with ruffles and a ribbon. Her clothing stands in stark contrast to Kio's much more casual clothing.
The Kaidou household appears to be one of significant wealth. When visiting the home, Kio remarks that it is, as it always was, a house of only women. It is a place where no one but women are allowed to live.
Much is unknown about Shikiko's background including where or when she was born, the relationship between her parents, and her role in the family.
Shikiko appears to be very independent for her age and quite mature. Upon greeting Kio she remarks on the lack of letters received from him as well as his lack of interest in the household. Her manner of speaking is seen as rude, but it is shown that she is trying to keep Kio's best interests in mind and not just trying to be selfish.
The maid, Katou, refers to Shikiko as Ojou-sama meaning young-miss or young-lady in Japanese. This marks Shikiko's position as a girl of high class in a wealthy home. Katou speaks to both Kio and Shikiko with the suffix -sama. This way of calling uses a respectful honorific for people of a higher rank than oneself.
When Kio asks Shikiko if they can speak in her bedroom, he is scolded by Katou. This characterizes the overall attitude of the house as quite formal and reserved. When Shikiko agrees to speaking with Kio in her room, Katou protests again.
At the instance of Shikiko's appearance in the manga, Kaidou Kio is revealed to be her father, a shocking plot point. Kio remarks that he has difficulty seeing Shikiko as his daughter due to the way that she acts and her age, which is quite close to his own. She was born without his knowledge in a location that he was unaware of.
Kio seems quite unwilling to add the suffix -san to her name when addressing her, marking his reluctance to address his daughter in such a formal manner.
Shikiko's attitude towards her father is quite playful and she does not treat him with respect, but as a lesser. When Kio points out that she is changing the subject to avoid his questions because she is uninterested in talking she quickly agrees. When he leaves, she thinks to herself that her father is a weak and sensitive man who she is protecting, not hurting. This dialogue implies that she knows the answers to some of his questions but is keeping them from him under the pretense of protecting him.
With no further explanation, Kio says that he requires Shikiko's permission in order to visit with her mother. No interactions are seen between Shikiko and her mother. At the end of her visit with Kio, Shikiko makes a mysterious remark while admiring a peony from Kio that the next flower belongs to her, after remarking, somewhat bitterly, that Kio prefers to take dinner with her mother.