After taking part in the National Middle School Tennis Tournament, 12-year-old tennis sensation Ryouma Echizen sets his sights on America to further develop his skills. Driven by ambition, Ryouma finds himself caught up in the perplexing circumstances surrounding his father's unexpected withdrawal from the professional tennis scene. Known as "Samurai Nanjiro," Ryouma's father was a renowned tennis player who allegedly retired after the US Open finals a few years prior. Despite scouring footage of the final match, Ryouma is still plagued by unanswered questions, and hopes to uncover the truth by witnessing the game firsthand. However, a supernatural twist intervenes, and Ryouma and his classmate Sakuno Ryuzaki are sent back in time to the US Open. Though events leading up to the finals seem normal at first, the mafia's involvement brings unforeseeable challenges, forcing Ryouma to overcome insurmountable odds and reveal the truth to prevent his father's career from being truncated.