Spirit of Steel

(The story is based on Super Robot Wars Original Generations & Iron Saga, with adjustments and modifications)
The world was once engulfed in a sea of flames caused by twelve humanoid giant machines,
later called the 'Grand Gods'.
Fast forward centuries and the war is but a legend forgotten by time - it is a memory that humanity can barely recall.
But then, the emergence of "Extra-Over Technology" suddenly jolts the entire world awake.
Forces of all manners and kinds conspire in the shadows,
all eager to lay their hands on this world-destroying technology
and they will rekindle the fires of war among the world's armies, mercenaries, and bounty hunters to get it.
Meanwhile, a normal teenage boy accidentally found a giant humanoid machine in the middle of turmoil. The legend of the normal boy turned-hero begins now!
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MC x Harem (Characters from various mecha-related media such as SRW, Iron Saga, etc)
Warning, rated M for violence (and might be some Lemon).