Yuka Sasaki presents herself as a cheerful student with superhuman strength, easily recognized by her blonde ponytail and constant necklace. Her friendly, expressive, and outgoing demeanor makes her popular and approachable. She shares an inseparable bond with Shinji Kazama, framed as childhood friends who grew up as neighbors and attended school together.

Beneath this facade lies a profound obsession and jealousy focused on Shinji. This fixation drove her to secretly follow Shinji and his girlfriend to a theater five years prior to the island events, where she set the building on fire. Shinji suffered severe burns rescuing others; Yuka then intervened, forcing open an emergency exit using her claimed strength to save him from asphyxiation.

Yuka's alleged talent for incredible strength is false. Her true ability is necromancy, enabling her to control corpses using personal belongings of the deceased. She maintains control over Shinji's reanimated body using a torn piece of paper from one of his tests, kept concealed in her rear pocket, while her visible necklace acts as a decoy. This power functions only at night or in pitch-black conditions and ceases at dawn or under illumination.

Her antagonism escalates when Nana Hiiragi exposes her lies. Yuka uses Shinji's corpse to repel Nana's initial attack, then mobilizes additional corpses of former students buried on the island to hunt her. She corners Nana in a mountain shack but refuses to enter, barricading the door until sunrise neutralizes her powers. Nana later steals the test paper keepsake and discards it off a cliff. She systematically dismantles Yuka's fabricated history: Yuka was not Shinji's girlfriend but a stalker, and the theater fire was premeditated murder intended to possess him post-resurrection. Psychologically shattered by these revelations, Yuka is killed by Nana using a poisoned needle.

Government assessments attribute a potential kill count exceeding 500,000 people to her capabilities.