Story

Humanity lies in ruins.
The Rapture invasion came without warning. It was both ruthless and overwhelming.
The reason: unknown. No room for negotiations.
In what seemed like an instant, the earth was turned into a sea of fire. Countless humans were hunted down and slaughtered without mercy.
None of mankind's modern technology stood a chance against this colossal invasion.
There was nothing that could be done. The humans were laid to waste.
Those that managed to survive found one thing that gave them the smallest glimmer of hope: the humanoid weapons.
However, once developed, these new weapons were far from the miracle everyone needed. Instead of turning the tide, they only managed to make a minor dent.
It was a complete and utter defeat.
Humans lost their homeland to the Rapture and were forced to live deep underground.

Decades later, a group of girls awakens in the Ark, mankind's new home.
They are the result of the collective technological knowledge pooled together by all the humans driven underground.
The girls board an elevator to the surface. It has not been operated for decades.
Humanity prays.
May the girls be their swords.
May they become the blade that enacts revenge for humanity.
Born out of mankind's desperation, the girls head to the world above, carrying the hopes and dreams of the human race on their shoulders.
They are code-named Nikke, a name derived from the Greek Goddess of Victory, Nike.
Mankind's last hope for victory.

(Official plot description)