In a flooded world, nations form "Azur Lane" to fight "Sirens". Factions "Union", "Royal", "Iron Blood", and "Sakura Empire" wield anthropomorphized warships from a "Wisdom Cube".

The seas were taken over by a mysterious enemy known only as "sirens". Humans then created humanoid female embodiments of real life warships in order to combat the sirens and take back ownership of the seas. Unfortunately, many human-like emotions were passed on to these warships, and a split occurred between these former allies. Separating into two groups known as Azur Lane and the Red Axis, these two groups now fight against each other. The Red Axis, comprised of warships from the likes of Nazi Germany (Ironblood) and Imperial Japan (Sakura Empire), has joined the evil sirens in their fight, utilizing advanced siren technology to obtain powers beyond that of their natural capabilities. Azur Lane, comprised of warships from the United States (Eagle Union) and the Royal Navy, still fights for the good of humanity, and believes the unnatural evolution of their Red Axis counterparts must be thwarted along with the sirens.—Riley R