The Greys appeared suddenly. They descended on the cities and destroyed the planet.
It was learned that they're drawn to female pheromones and would ravage women to sexual exhaustion. Women were quarantined in shelters.
A female doctor found a way to manufacture the pheromone, and built a weaponized suit that only a woman with a strong libido could wear.

"You have been chosen. From today, you will become FElmina the Awakener and fight the Greys."

"Why me?"

"This suit requires someone with your extremely rare levels of craven endurance!"

"That's... not exactly a compliment, is it."

Put on the suit and begin the fight to save the world......

[From DLsite English]