Yuki Sexaroid is the medical officer aboard Big One, and is actually a type of robot called a Sexaroid. In the beginning of Season One of the Galaxy Railways she firmly believes her role is to be the medical officer and that because she isn't human she can't love or be involved in anything that doesn't have to do with duty. But as the season progressed, she began to realize that being human was a state of mind, not matter.
Yuki is also a protagonist in the mini series, "Kitsandra Katswell's Adventures of Galaxy Railways", although she did make a cameo appearance in Kitsandra Katswell's Adventures of Sleeping Beauty, which also starred Big One, who she views as a fatherly figure, since he too, is a machine.
Even though she is typically prone to be devoted to her duties as a medical officer, Yuki has shown that she does have a kind, caring side to her. She used to shy away from social activities because she believed it interfered with her medical duties. Since then though, she has learned to loosen up and enjoy life while it lasts.
Yuki is a tall, beautiful woman. Her skin is peach-colored, she has long blond hair that goes down to her feet, and the end of it is tied with a red ribbon. She wears a skin-tight white body suit with blue and red details.