When she was five years old, Yukio predicted the death of her own parents. When the event came to pass, Yukio was left orphaned. Discovered by Ichirō Yashida, she was brought in to be the friend of Mariko. The two became best friends, caring for each other like they were sisters. Yukio was also trained as a ninja in order to protect Mariko.
When Yashida gained a terminal illness, he sent Yukio to find the Wolverine. Eventually finding him, she managed to coax him to return to Japan. Staying by the Wolverine's side as he unraveled Yashida's conspiracy, Yukio had an epic battle with Dr. Green, also known as the Viper. For a while afterwards she traveled with the Wolverine as his bodyguard, however, eventually they parted ways.
Yukio had a rare form of telepathy that allowed her to predict the future. However, specifically it was only the deaths of certain individuals whom she knew.