The Secrets from the Abyss: Origins

In an alternate 1941, the Pacific War is won by the Imperial Japanese Navy. Follow rear-admiral Fujioka Sekimoto and his protégé Lt. Commander Asuka Shiba as they learn to face an enemy much greater than anything humanity has witnessed and the beginnings of the newly developed creation, 'Ship Girls'. What is the secret behind this 'Abyssal' fleet?