Gekitotsu no Hexennacht - Volume 4, Chapter 11: Can I Pass?

Florentia was reincarnated as the illegitimate child of the richest family in the empire.

A Mysterious continent, with many powerful sect and countless strong one. Juvenile Zhou Heng with a mysterious black broken sword, from the original stone town out into this world of war. Ascended the throne of the world with only a sword in hand.

- Description from Novelupdates

A mecha otaku is reincarnated into another world as Ernesti Echevalier (Eru). In this world there exist huge humanoid weapons known as Silhouette Knight. Dreaming of piloting those robots, Eru, with childhood friends, Archid Walter and Adeltrud Walter: together they will aim to become a Knight Runner, pilot of Silhoutte Knight.

The formless ancient world was infested with despicable demons. They hunted and feasted on mankind, keeping the human civilization constantly in a weak and suppressed state.