The 50th Black Swan; the first Black Swan to be able to completely neutralize Strauss' power. She wants to protect her grandfather by controlling the vampire king, but is often unsettled by Strauss' enigmatic nature. Her face bears an uncanny resemblance to Yuki's (the 49th Black Swan), although their personalities are quite different. Like her grandfather, Kayuki was first introduced wearing a mask because she was ‘shy’.
Kayuki sometimes delves into the Black Swan's accumulated memories to gain a better understanding of Strauss; however, the Black Swan has few memories of who Strauss is as a person. Kayuki knows that such actions will cut her already shortened lifespan. She has shown several instances of sympathizing with Strauss and wanting to learn more about him as a human, even to the point that she doubts her goals. These actions eventually make it hard for her to kill him. Strauss is aware of her shortening lifespan in pursuit of knowledge and warns her against it, trying to force her to view him as an enemy rather then a friend in order to spare her the pain when his death comes. While Kayuki is extremely mature for her age, she is not always in perfect control of herself. On several occasions, Kayuki attacks Strauss out of anger or in an attempt to discipline the disobedient vampire king. Her level of stress continues to build because of the tension from watching Strauss and the extensive use of the Black Swan’s powers. Strauss predicts she will die far sooner to than any of the previous Black Swans. She is always seen wearing a kimono. After she learns of the entire truth about Strauss, she finally understands him, and she falls in love with him. Despite her feelings, she cannot avoid her destiny.