Ernesti, a programmer and mecha fan in his previous life, is reincarnated in a fantasy world where he sets out to pilot a humanoid weapon.

A mecha otaku is reincarnated into another world as Ernesti Echevarria, also known as Eru. In this world, huge humanoid weapons known as Silhouette Knights exist. Dreaming of piloting those robots, Eru and his friends, Archid Olter and Adeltrud Olter, aim to become Knight Runners.