Azur Lane is set in an alternate timeline where the seas are dominated by a mysterious enemy known as the Sirens. To combat this threat, humanity creates humanoid female embodiments of real-life warships, called shipgirls, who possess the spirits and powers of historical warships. These shipgirls form factions including the Azur Lane (primarily the United States' Eagle Union and the Royal Navy) fighting for humanity’s good, and the opposing Red Axis (including the Ironblood, representing Nazi Germany, and the Sakura Empire, representing Imperial Japan), which has allied with the Sirens using advanced Siren technology to gain unnatural powers. The conflict revolves around these factions battling each other and the threat of the Sirens in the hope of reclaiming the seas.