Yuki stands as a central figure in the narrative, distinguished by waist-length blue hair, vivid blue eyes, and a sleeveless white dress featuring an orange bow at the front. An identical orange bow adorns her hair, complemented by a silver triangle necklace.

She hails from the vanished city of Lost, destroyed in a catastrophe, and remains its sole known survivor. Her father Daichi—a researcher of parallel worlds—and younger brother Souma disappeared during the city’s fall. Afterward, Akira became her guardian, raising her and Souma. Yuki’s journey begins upon receiving a communication from her missing father, compelling her toward the ruins of Lost.

Yuki wields mysterious abilities tied to her survival and Lost’s secrets, manifesting as protective barriers that shield herself and others from harm—proven when she deflects disaster during a helicopter crash. This power attracts pursuit from a shadowy organization intent on suppressing truths about Lost’s disappearance.

Her journey anchors the story. Initially reliant on protection—especially from Takuya, a courier assigned to escort her—she gradually asserts agency. Their alliance thrives on shared survival and the quest to uncover Lost’s fate and locate Daichi. Opposing forces, including agents like Suzuna and the Phantom Thieves, relentlessly obstruct their path. Key relationships define her: Takuya as protector and companion; Akira as her nurturing past guardian; and Daichi as her driving purpose.

Yuki evolves through escalating determination and resilience. Facing relentless threats and fragmented revelations about Lost and her origins, she transforms from a vulnerable figure into an active challenger confronting perils alongside Takuya. Her resolve solidifies throughout the ordeal, fueled by the twin goals of family reunion and understanding the city’s annihilation.