IJN Shoukaku was sunk by an American submarine on June 19, 1944. The name of the sub is USS Cavalla. A Gato class submarine. The incident happened off the shores of the Marianas Trench.

Four months later her sister ship the IJN Zuikaku was sunk by aircraft bombardment. Most of which came from her nemesis USS Enterprise (CV-6) on October 25 1944. But after the war Enterprise was turned into scrap metal several years later.

Most of the steel was used to build the first nuclear powered aircraft. The eighth ship carrying the name of the most decorated warship. USS Enterprise (CVN-65). However in a different world. Both of them are now part of an alliance called Azur Lane.

Many years has passed and peace in the alternate universe is well maintained after the Sirens have been defeated. Meanwhile in the original world. Peace is once again threatened. The Sirens have returned and pushed humanity out of the waters again. They decide to spare the Philippines since it is the only country with no capable naval fleet. The Pinoy fisher folk benefited from the Siren attacks.

They can move in and out of the West Philippine Sea without fear of being bullied by Chinese vessels. The first world country has ordered all of its fleet in their so called 9 Dash Line to return to the mainland and defend its territory against the alien invaders. All is left is a meager force defending their man made island bases. However all four bases eventually fell to the Siren attack. The Philippines benefited from the attack as the government placed chunks of it's armed forces in the man made island bases. Once again the ship girls of Azur Lane have been called into action. Except for two girls who's returned to their original form and were still in the bottom of the sea.

Time Skip:

The year is 2024 and the Sirens have returned after an eighty year hiatus. They may have taken a long time in attacking the Earth. But the timing was perfect as almost of the ship girls that they have fought are either in the bottom of the ocean. Or turned into ship museums. The world is on a defensive as the Sirens have staged multiple attacks on different countries. Except the Philippines. With their high tech warships still rendered ineffective against the extra terrestrial beings. All of the different countries relied on their ground troops and air assets to fend off the alien invaders.

The victory was temporary as the Sirens ceased their attacks. A hotshot Top Gun fighter pilot and his carrier strike group has been assigned to Azur Lane headquarters. He is now on a vacation leave and is returning to his motherland. He is a Filipino citizen serving in the US Navy. And he will soon meet the two girls who are actually the two Japanese aircraft carriers who were sunk in 1944. One of them is already rising up again from her long slumber. She and her sister will meet the Filipino hotshot pilot while they're manning a small ramen shop and restaurant.