Knights & Magic by Amazake No Hisago

Translated from Japanese Action Comedy Fantasy Romance Adventure School Life Harem Magic Swords Mecha
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 Walter and Adeltrud Walter: together they will aim to become Knight Runner, pilot of Silhoutte Knight.

1: Knights & Magic