It's about a girl named Hikari Kamijou who dreams of becoming a national rhythmic gymnastics champion.

Hikari no Densetsu is primarily a love story that it is set in the late 80s junior high school atmosphere. The plot revolves around four characters and how they work to achieve their dreams. Hikari Kamijou, a young, naïve, care-free, young woman who dreams of becoming an Olympic Champion in the sport of rhythmic gymnastics ever since she witnessed a performance of the young Diliana Georgieva (a champion Bulgarian rhythmic gymnast). And while she performs poorly and is not very confidant in her skills as a rhythmic gymnast, she is very passionate about the sport and shows occasional brilliance during her performances.

From Wikipedia