Sayumi Nishii comes from Osaka, Japan. She moved to Tokyo at the age of six and began her ballet training at the Matsuyama Ballet School, which she continued at the Chie Tomioka International Ballet de Tokyo. In 2007, she moved to Italy and completed a year at the Scuola di Ballo dell' Accademia Teatro alla Scala in Milan. The dancer then completed her dance training at the Zurich Opera House Ballet School.

Her professional career initially took her to the National Theater Brno in the Czech Republic, where she became a member of the corps de ballet. There she had the opportunity to dance in choreographies by renowned choreographers such as Uwe Scholz, George Balanchine, Youri Vamos and Lukas Timulak.