Sakumi Nakahara, a teenage girl, contacts the protagonist upon discovering his photographs and contact details in a motorcycle magazine. She sends handwritten letters detailing fantasies about him passing her residence, exposing profound isolation and emotional vulnerability. Her correspondence consistently reveals loneliness and a yearning for connection, though her specific circumstances or family background remain unknown.

Her room is visually defined by hazy, pastel tones and soft lighting, contrasting sharply with the narrative's darker settings. This aesthetic frames her as an idealized yet distant presence in the protagonist's thoughts.

Progressing through the story, Sakumi sends another letter announcing her upcoming birthday and requesting a phone call precisely at 6:00 PM on August 10th, including her current number. This leads to a pivotal moment where the protagonist intends to answer but fails due to conflicting obligations, leaving the call unanswered and their connection unresolved.

Sakumi operates solely through written communications, functioning as both narrative device and emotional mirror. Her physical form never appears; her background, motivations, and fate surface only through letters and the protagonist's interpretations. Her arc concludes ambiguously after the birthday call, with no further interaction or resolution.