Osaka, 1938. Fuku-chan, a high school graduate and the youngest of three sisters, lives with her mother, Suzu, and eldest sister, Saki. To support her family after her father's early death, Fuku-chan starts working as a hotel telephone operator. The first call she takes is from Mampei, the man who will become her husband. Together, they are destined to create the invention of the century.

Fuku-chan's mother, Suzu, suddenly collapses, complaining of a stomachache. The middle sister, Katsuko, suspects she's faking it, while a panicking Saki exclaims, "This is no time for marriage!" Too worried to focus, Fuku-chan mistakenly connects a call from Mampei to a foreign guest—a major blunder. An upset Fuku-chan returns home to a surprising sight.

Fuku-chan and Katsuko are confronting Suzu, who is secretly eating canned tuna despite her stomachache. Saki explains that their mother's reason for lying is that she does not want to be alone with Fuku-chan. While Fuku-chan is shocked to learn that she is the cause of the problem, Mampei, who is struggling to run his business, is approached by a man named Kajitani.

Fuku-chan is delighted that Suzu finally approves of Saki's marriage. Wanting to do something special for the wedding, she visits a place recommended by her best friend, Toshiko. There, she meets Mampei, who develops slide projectors. With his help, Fuku-chan plans something truly special.

Three years have passed since Saki's wedding. Fuku-chan has become accustomed to her front desk job. One day, she helps out at a party held by the Osaka Chamber of Commerce and Industry. As she is helping a man dry his pants, which he inadvertently got wet, he asks her if she is Miss Imai. Confused, she takes a closer look at his face... He is Mampei, who has now become a successful businessman.

Fuku-chan visits Saki, who has caught a cold. On her way home, she runs into Mampei, and they decide to have ramen noodles together. They realize during their conversation that Fuku-chan had answered Mampei's call three years ago when she was working as a telephone operator. Fuku-chan is flustered while Mampei believes it must be fate.