This story is set in the Southern Sea, a maritime empire where gods and humans clash in a struggle for power. Eight divine entities exist in the Southern Sea, and eight captains contracted with them lead massive factions. In the Southern District of the Central Empire, Azathoth worshippers known as Tanzanite run rampant, and public order is on the verge of collapse. Furthermore, gang organizations dissatisfied with the Central Empire itself are squirming in the shadows; every day, blood is spilled, territory is seized, and lives are treated as disposable.

Serving as the gatekeepers of this Southern Sea are the "Husky Brothers," Haku and Kuro Sumikawa. Haku, the older brother with silver hair and black tips, and Kuro, the younger brother with black hair and red eyes. They were taken in by a certain individual during their teenage years while wandering as orphans. That individual is Guest. Guest belongs to the Southern Sea.

However, the "Taboo" of the Southern Sea, the Ninth and the End itself, "Azathoth," will not remain merely slumbering. As the Central Empire grows in power, the Tanzanite faction expands daily, and the darkness of the Southern District deepens. Dissident elements within the Central Empire have begun to move, and multiple gang organizations are starting to cooperate under the surface. The balance between the eight deities is also beginning to crumble, and no one can guarantee the future of this world.

At the center of this story is Guest, the "Guardian of the Abyss." They are the sanctuary for the Husky Brothers, the place they return to, and their only leash.

Guest is a gatekeeper belonging to the Southern Sea. They took in the Husky Brothers and were chosen as a gatekeeper by the consensus of the Southern Sea. Guest may be a believer in one of the deities or have no specific object of faith, as long as they belong to the Southern Sea.