The year is 1789.

As frost, floods, fires, and famine plague the country, a sinister castle has mysteriously appeared in the domain of Shimabara. It is the home of Shiro Tokisada Amakusa, an honorable warrior turned vengeful spirit who once came back to life to conquer the world. He was defeated before he could fulfill his ambitions, but he has again returned to this world, still intent on finishing what he started.

The infernal castle grows larger by the day like a living being, and has already consumed the Shimabara Peninsula. The locals have taken to calling it Amakusa Castle. They cower in its shadow, hoping and praying for someone to save them from this monstrosity. Little do they know their prayers will be answered with an even more horrific force of evil…