Hayakawa Yui is completely unmotivated and lazy, loving nothing more than sleeping and eating. Although she is 16, she resembles an elementary school boy; her sole talent is running at high speeds. After accidentally activating a time machine built by her younger brother, she travels to the Sengoku period, where she fortuitously joins a group of retreating foot soldiers under the alias Yuinosuke. She then consumes some amanitas and encounters the man of her dreams.