The Defenders of Humanity (XCOM x NIKKE x Azur Lane)

Note: This is my first book. If there's something you believe is badly written, don't hesitate to tell me.

In a world different from ours, mechanical beings called raptures have invaded the entire earth and almost killed all of humanity, causing the remaining survivors and what's left of a Goverment to hide in an underground city called The Ark, where they still are to this day.
Inside, however. 2 Commanders, each from factions not related to The Big 3, are still around and hiding, waiting to be back on the fight for humanity. But 1 mission with a certain rookie Nikke Commander Will change both his, and their lives.
The question being:
What will happen when the Central Goverment rediscovers these 2 old factions?

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