At the age of four, she entered Tokyo University of the Arts, having been selected under a programme aimed at providing specialist education to gifted children.
At the age of nine, she made her orchestral debut, playing with the Tokyo New City Orchestra.
[1] In 1993, she moved to Germany to study with Karl-Heinz Kämmerling, and later with András Schiff.
The German magazine Fono Forum gave a five-star rating to her recording of the Chopin Etudes, made when she was sixteen years old.
Reviewing the recital, the critic of CultureCatch praised the "beauty and great variety of Kosuge's tone production".