Inspired by his tennis champion father, Ryoma is determined to train in the US after winning a championship in Japan. He runs into his classmate Sakuno right as she is getting into trouble with street gangs, and Ryoma accepts a tennis match against the villains to save her. During the intense tennis battle, the shock of two tennis balls ramming into one another disrupts the flow of time! Ryoma and Sakuno suddenly find themselves transported back into the past, decads, before, when Ryoma's father challenged his last match at a championship in the US.