Read Knights & Magic manga
A mecha otaku is reincarnated into another world as Ernesti Echevalier (Eru). In this world, exist huge humanoid weapon known as Silhouette Knight. Dreaming of piloting those robots, Eru, with childhood friends, Archid and Adeltrud Olter: together they will aim to become Knight Runner, pilot of Silhoutte Knight. Based on Knights & Magic Novel.