Legend of Hikari

(from ebookjapan):

Joining the Rhythmic Gymnastics Club, a fateful encounter ensues! Hikari Kamijo transfers to Aika Junior High School, where she fatefully meets the next Rhythmic Gymnastics Queen, Hazuki Shiina, and the Gymnastics Club's Hope, Takaaki Oishi!

In the midst of a crowd of top athletes, Hikari faces an athlete selection test to compete in a national junior high school competition....　

This is the first volume of the rhythmic gymnastics manga that was a big hit in Weekly Margaret in the 80's, depicting the agony and love of an athlete with a flexible brush stroke!