Once, there was a great war. A memory from the distant, ancient past.

And now. Humanity uses weapons called Kanmusu (Shipgirls) to fight a war against an enemy of unknown origin and purpose called the Abyssal Fleet.

Kanmusu: The basic weapons in the anti-Abyssal war. Their appearance and class vary. They are treated as "ships" and have no human rights. A single destroyer girl has firepower and speed equivalent to the warships of WWII.

Abyssal Fleet: An enemy of unknown origin. They attack all humans in sight with overwhelming numbers. They usually stay in their territory but periodically lead large forces for expansion or landings. When their numbers grow too large, weaker individuals are pushed out and begin attacking fishing boats, transport ships, shipgirls, and ACs.

Admiral: The head of a "District Headquarters." A grueling middle-management job involving shipgirl operation, mental care, and paperwork.

Mercenaries: Humans who pilot ACs. Their skill levels vary, and they often deal with betrayals and friendly fire over rewards, but the pay is excellent.

Asaniwa Theater: A massive facility for mercenaries and ACs. Mercenaries exchange info at the bar, eat at the cafeteria, pick missions and get details from Samidare, or sleep in the dorms. The main hall's theater plays movies 24/7.

Imperial General Headquarters: The central organization for humanity's strategy against the Abyssals.

GHQ-Affiliated ACs/Shipgirls: They take command on-site during Abyssal landings. Rumors about them are rarely good.

AC (Armored Core): 5-meter-tall piloted humanoid weapons. Agile, but one unit is only a match for one shipgirl. Excavated weapons from ancient wars. Mostly a mystery, they are salvaged, armed, and deployed. Boosters allow for 3D combat via hovering and gliding. Comes in Light, Medium, and Heavy types. The cockpits are painfully cramped.

Bipedal: The most versatile legs. Can handle sea combat, landing prevention, and sniping. Reverse-Joint: Bird-like legs. Low defense/firepower but high jumping power to confuse enemies. Used during landings. Quadruped: Multi-legged tank structure. Rugged design like a mobile turret. Uses stakes to stabilize for sniping. Mainly for coastal defense and landing prevention.