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—Eagle Union, Royal Navy, Sakura Empire, and Iron Blood—formed Azur Lane, paving the way for the improvement of modern warfare, which led to an initial victory against the common threat. However, this tenuous union was threatened by opposing ideals, dividing the alliance into two. Sakura Empire and Iron Blood broke away and formed the Red Axis, 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. Meanwhile, Javelin, Laffey, and Unicorn—three ships from the union—stumble upon Ayanami, a spy from the Red Axis. Strange as it may seem, they try to befriend her, but as enemies, their efforts are for naught. Still, they persevere in hopes of succeeding one day. 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.

Cyress is a peaceful place. People are going about their lives. Two lovers embrace, a family throws a birthday party for their child, a group of people party at a local restaurant. But suddenly, their surroundings explode into smoke and flame. A group of terrorists has snuck through the planetary defenses and has begun an assault. Defenseless, there is little the people of Cyress can do. As the military scrambles to discover what happened, the terrorists manage to hijack seven PDP missiles, which are capable of destroying an entire planet. These terrorists, who call themselves Solomon can now hold entire planets hostage! They must not be stopped. (Source: Themanime)

In a seemingly peaceful time without looming threats of Sirens or war, shipgirls from different nations live together in harmony. Some girls, such as the destroyers Ayanami, Javelin, Laffey, and Z23, attend school. Others immerse themselves into various other activities, including sports, foraging, training, going to formal parties, or even vying for the commander's attention! But one thing is for certain: the girls will continue to deepen their friendship in the pleasant port of Azur Lane!

Sequel to Battle Spirits: Kakumei no Galette.