Sayoko "Arashi" Arashiyama is a World War II-era ghost perpetually appearing as a sixteen-year-old girl. Her mission drives her to travel back in time to save her community from wartime air raids. Activating this time-travel ability requires physical touch with a living person from the present. This necessity forms her connection to thirteen-year-old Hajime Yasaka, whom she meets at the Ark café. Their bond facilitates joint journeys through time, revealing intricate layers across events.

Her personality blends a strong sense of righteousness with a good sense of humor. She exhibits forgetfulness and impulsiveness, often acting without forethought. Arashi shares an extremely close friendship with fellow WWII ghost Kaja Bergmann, who serves as both confidante and a contrast to Arashi's lively nature.

Time-travel interactions reveal her first love to be Hajime himself, adding temporal complexity to their relationship. Daily life involves working alongside Hajime and others at the Ark café, where comedic and supernatural incidents occur. One recurring scenario involves attempts to consume expired milk by taking it to the past before its expiration date.

Her name reflects her character: "Sayoko" combines the Japanese characters for "small," "night," and "child," while her surname "Arashiyama" derives from "storm" and "mountain," aligning with her storm-related nickname "Arashi."