Goetia was defeated, and the human order was saved from incineration. For such a heroic feat, Ritsuka Fujimaru, the younger of the Fujimaru twins and one of the key masters of the effort was repaid in the Clock Tower with treachery. Unwilling to accept such an outcome, two Avengers defied fate to give her a new chance, a new life in a timeline still in the age of the gods.

A Shipgirl base requires a lot of ships. Some battle against the Sirens. Others run supply missions. And many sacrifice their rigging and station so others can fight better. Deprived of purpose, and left cut off from the life they knew. At least until disaster strikes the main fleet, and they're called back into emergency service.

Questioning only briefly why he's there anyway, a human from the real world ignores the rules of the game and drags Oscar of Astora on a grand adventure to discover the truth of the conflict between Light and Dark. But more importantly to impress his waifu.