Disclaimer

An unknown enemy called the Sirens are wreaking havoc around the world. Azur Lane, a multinational military alliance, was formed to fight against The Sirens.
However, when the world are fighting The Sirens, a faction called Crimson Axis declared war on Azur Lane and thus a "civil war" began. These two fighting each other due to different ideology. It was at this time, unknown fleets of unknown origin are trying to unite the two opposing factions together and fight the Sirens once and for all.

Disclaimer: I do not own Ace Combat nor Azur Lane.