TOKYO — Keiko, a defiantly oddball 36-year-old woman, has worked in a dead-end job as a convenience store cashier in Tokyo for half her life. She lives alone and has never been in a romantic relationship, or even had sex. And she is perfectly happy with all of it.

Her creator, Japanese novelist Sayaka Murata, thinks that makes Keiko a true hero.

“Keiko doesn’t care — or maybe she doesn’t realize — when she is being made fun of by others,” said Ms. Murata, 38, of the narrator of “Convenience Store Woman,” her 10th novel and first to be translated into English. “She did not want to have sex at all and that was fine with her, and she chose that life. I really admire her character.”

“Convenience Store Woman,” which won Japan’s prestigious Akutagawa Prize for literature two years ago and has sold close to 600,000 copies here, will go on sale this month in the United States. Written in plain-spoken prose, the slim volume focuses on a character who in many ways personifies a demographic panic in Japan.

Japanese media is filled with stories about declining marriage and low birthrates, as well as references to ominous surveys about young people who are virgins or have forsaken dating and sex, a narrative that the Western press finds particularly alluring when writing about Japan.