When the "Sirens," an alien force with an arsenal far surpassing the limits of current technology, suddenly appeared, a divided humanity stood in complete solidarity for the first time. Four countries formed Azur Lane, paving the way for the improvement of modern warfare, which led to an initial victory. However, this tenuous union was threatened by opposing ideals, dividing the alliance into two and humanity became fragmented once again.
As a seasoned and experienced fighter, the "Grey Ghost" Enterprise shoulders Azur Lane's hope for ending the war. But behind her stoic persona hides a frail girl, afraid of the ocean. Even so, she continues to fight as she believes that it's the only purpose for her existence.
Amidst the neverending conflict within humankind, the keys that could unite a fragmented race might exist: a soldier coming to terms with her mysterious personality and camaraderie between those with different ideals.