The "hottie from the crime lab" as she is often referred to be Ranmaru's colleagues. Her mother died prior to the Machida incident, with her father becoming obsessed with his research soon after. Saya set her and Ranmaru up on a blind date that ended up in them finding out more about the phantoms. Later on, on a second date they were attacked by Yukino's father after he turned himself in a hybrid of human and phantom. Leaving her job awhile after, Yukino gives Ranmaru the info behind the murderer of her mother who caused the Machida incident. (Wikipedia)