Tsubasa Kurata, a company programmer and a mecha model fan, is killed in a car accident. Tsubasa is reincarnated as a young boy named Ernesti "Eru" Echavalier in the Fremmevilla Kingdom in a world where magic exist. After witnessing his father Mathias defeating a demon beast in a mech called Silhouette Knight, Eru is motivated to be a Silhouette Knight pilot - Knight Runner - so that he too can ride one as well.