The year is now 1946.
World War Two has been over for little more than a year now in Europe. Germany has already surrendered and the Nazis are even now facing Allied justice. The nightmare is at last over and people are finally able to rebuild and begin anew. On the other side of the globe, however, a new war has already started. A whole new kind of horror for the various peoples of the Pacific.
The Abyssal War.
It has been roughly two years since the Abyssal Fleet first emerged from the heart of the Pacific Ocean. Armed with advanced technology second to none, they easily swept through the seas, sinking ships and even entire fleets of all allegiances. They further terrorized the coastlines and frequently interrupted military supply lines with their mere presence alone. So great was the threat they presented that their arrival forced the Japanese Empire and the United States - two embittered nations who had been at war with each other since 1941, to agree to a ceasefire and even an alliance.
Both sides in some way benefited greatly from joining forces against the Abyssal Fleet. The United States was generously conceding excess supplies courtesy of its massive industrial reserves to the Japanese who faced a much stronger opposition from their new common enemy. Japan had severely depleted much of its own resources during the Second World War and this new source of raw materials and goods allowed it to endure the unrelenting assault from the Abyssal Fleet.
It was both a sign of goodwill and pragmatism though. The US understood that if Japan fell, then the entirety of the Abyss would promptly direct its might toward the American coastline. However, aside from this liberal exchange of resources to their former enemy, the USN kept mostly to its own borders and ships rather than go out of its way to assist the IJN in defending the Japanese home islands. Repelling the Abyssal attacks took a heavy toll on their fleet and the majority of American commanders still held some reservations on helping a nation which only months ago was their sworn foe.
The Japanese meanwhile were providing the American forces with something of considerable value in return for the much needed supplies: Intelligence. While the first official encounter with the Abyssal Fleet had been in the middle of 1944, the Japanese Navy had been aware of unidentified vessels roaming the open oceans as far back as 1942. Most of these earlier sightings were of smaller ships - nothing of firepower greater than a light cruiser, but the size and scale of the ships they reported quickly grew at a distressing rate over the following couple of years. Even so, these initial observations of the enemy had allowed the Japanese to discover patterns in the Abyssal Fleet's behavior. Drawing upon these early experiences, the IJN had developed tactics and formations which proved vital for the USN at fending off the alien vessels with significantly reduced casualties.
However, the IJN had not divulged all of its findings with the US Navy. They had cautiously decided to withhold their most important breakthrough on the Abyssal Fleet. After examining various remnants left over from damaged and destroyed Abyssal ships, the Imperial Navy had developed its own weaponry, reverse-engineered from the superior Abyssal technology and designed specifically for one purpose: Countering the Abyssal Fleet. They were known as "Kanmusu"; human-sized weapon platforms each wielding firepower comparable to an entire warship. Far more maneuverable than any conventional vessel not to mention just as durable, they were a real key in the IJN's ability to stave off the relentless waves of Abyssal ships rolling upon their borders. But only just.
The nature of the kanmusu was not at all confidential though. The US was more than well aware of their existence and quite envious of their incredible performance record against the Abyssal Fleet. The USN repeatedly badgered the IJN into sharing the technologies required to produce these game-changing weapons. Each attempt however, was unsuccessful and only further strained the tense relationship of the two nations. The Japanese meanwhile, tried to convince the US to send aid to help defend their coastlines. These talks likewise, had similar results.
It was only in the late summer of 1945 that the Americans finally came up with a compromise to the impasse. The USN would no longer question the IJN for the secrets involved in developing kanmusu. Furthermore, they would even begin posting some of their fleets around Japanese territories to assist in coastal defense. But in exchange though, the IJN would have to allow a certain amount of their kanmusu fleets be commanded by a USN officer. It was a difficult choice for the Japanese Navy; either they surrender a portion of their greatly coveted kanmusu to the Americans anyway, or refuse and let their coastal defenses be overwhelmed by the steadily increasing Abyssal Forces.
Reluctantly, the IJN eventually accepted these terms. Allowing a few foreign COs into their fleet was preferable to letting their borders be overrun. As a gesture of both nations' commitment to the war effort, these new joint task groups were then promptly issued a special assignment. A mission that would hopefully, alter the defensive nature the war was taking. The order given was simple:
Take the fight to the enemy's waters.
The counterattack against the Abyssal Fleet was finally underway.