Tsukasa Fujii is a supportive figure and close confidant to the male protagonist, distinguished by his slim build, average height, and black-blueish hair that grazes his nape, with bangs swept to frame the right side of his face. His features are accentuated by transparent rectangular glasses and dark-blue eyes.

Born on October 1, 1999, he attends the same Tokyo high school as the protagonist, sharing classes and mutual friends. His demeanor balances a stern exterior with genuine concern, particularly when detecting abrupt shifts in the protagonist’s behavior during supernatural body-swapping events. Though initially puzzled, he steadfastly provides guidance and aid.

He joins the protagonist and a companion on a quest to locate the rural town of Itomori, traveling to Hida and Takayama while painstakingly cross-referencing landscape sketches to pinpoint the area. After uncovering Itomori’s destruction, he continues collaborating with others to mitigate the fallout of the comet disaster.

By the story’s conclusion, he marries Miki Okudera, the protagonist’s coworker—a detail solidified through director interviews and supplementary materials.