Haruka Sakimizu is a tutor burdened by profound emotional trauma after a student under her supervision died, leaving her haunted by guilt and recurring nightmares. Seeking respite during a vacation, she retreats to a secluded mountain resort. When a snowstorm traps her and other guests, she forms a romantic involvement with Satoshi Suzusaki, the central detective figure. Their intimacy escalates against rising danger, including explicit encounters in Episode 3.

As brutal murders plunge the resort into chaos, Haruka evolves from a peripheral presence to an active investigator. Her perceptiveness uncovers inconsistencies in guests' accounts, aiding Satoshi's pursuit of the killer. Despite vulnerability from her trauma, she confronts her fears and leverages observations to help solve the mystery.

Her relationship with Satoshi anchors her emotionally while serving as a narrative device that unveils fragments of his obscured memories. Throughout the ordeal, her unresolved trauma intertwines with the present danger, directly influencing her interactions and decisions.