After the sudden arrival of the highly advanced alien menace known as the Sirens, humanity set aside their disagreements to form an extraordinary coalition. The Eagle Union, Royal Navy, Sakura Empire, and Iron Blood united to establish Azur Lane, which initially achieved victory over the Sirens using cutting-edge military technology. But ideological rifts soon split the coalition apart. The Sakura Empire and Iron Blood seceded to create the Red Axis, plunging humanity back into conflict.
Enterprise, the hardened and war-weary "Grey Ghost," carries the hopes of Azur Lane to bring the war to an end. Beneath her stern facade, she struggles with a profound fear of the ocean. Still, she presses onward, convinced that fighting the Sirens is her only purpose. Meanwhile, three ships from the union—Javelin, Laffey, and Unicorn—meet Ayanami, a spy working for the Red Axis. Despite their opposing sides, they work to build a friendship with her, trusting that their connection might one day heal the rift.
In the middle of the ongoing turmoil, the key to reuniting humanity may rest with a soldier wrestling with her own mysterious past and the bonds formed between those who hold different beliefs.