Ryo believes she is an ordinary girl leading a typical high school life in modern-day Tokyo. But is she? During a school trip, a mysterious man attacks her, claiming to be Benkei, the legendary warrior monk who collected 999 of his opponents' swords in battle during the Heian era. He also claims that she is Ushiwakamura, the 1000th opponent who, according to folklore, defeated Benkei and became his master. But... Ushiwakamura was a man! And Benkei and Ushiwakamura lived in 13th-century feudal Japan!