Hayakawa Yui is 16 years old. She's only good at running but is having a bright high school life. However, one full moon night, a time machine created by her brother, Takeru, sends her to the Warring States era. Yui is confused when she awakens but manages to acquire armor and mix in with the Ashigaru Corps. She claims her name is Yuinosuke. Although she is despairing, she falls in love at first sight with a young warrior that appears in front of her. He is the oldest son of the Hagi family of the Sengoku Daimyo, Hagi Tadakiyo.