When the "Sirens," an extraterrestrial force wielding weaponry far beyond the scope of current technology, appeared without warning, humanity set aside its divisions and united for the first time. Four nations—the Eagle Union, Royal Navy, Sakura Empire, and Iron Blood—established Azur Lane, advancing modern warfare and securing an initial victory against their shared enemy. However, clashing ideologies soon threatened this fragile alliance, splintering it in two. The Sakura Empire and Iron Blood seceded to form the Red Axis, and humanity once again found itself divided.
A seasoned and battle-hardened combatant, the "Grey Ghost" Enterprise carries Azur Lane's hopes for ending the war. Yet beneath her stoic exterior lies a vulnerable girl who fears the sea. Still, she continues fighting, convinced that this is her only purpose for existing. Meanwhile, three ships from the union—Javelin, Laffey, and Unicorn—discover Ayanami, a spy from the Red Axis. Though their efforts to befriend her seem futile given their opposing sides, they persist, hoping their friendship might one day prevail.
Within humanity's endless conflict, the keys to reuniting the fractured race may exist in a soldier coming to terms with her mysterious nature and in the bonds of camaraderie between those with opposing ideals.