Taken from Riboninfo:
Karin is a student of an institute that's very strict, but then leaves class to be dedicated to street dance in a club called "Free Square," that is in fact, one of the best. One day while dancing with her friends a group of boys who play basketball arrive and Karin falls in love at first sight with their leader, Yuuma Seta. Some thugs want to be in the club and Yuuma challenges them to a game of basketball, but the thugs are cheating...
The prequel to this story is called Pop n' Eight Beat.
