Yumoto was born in Tokyo and graduated from Tokyo College of Music. She began writing scripts for opera and became a writer for television and radio. Her debut children's novel ""The Friends" (1992)" received the Newcomer Award from the Japan Children's Literature Association and the Boston Globe–Horn Book Awards in 1999. It was adapted to a movie in 1994, directed by Shinji Sōmai. "Kishibe no Tabi" (Journey to the Shore), another of her books, was adapted to a film; directed by Kiyoshi Kurosawa, it won the Un Certain Regard award at the 2015 Cannes Festival.