It is the fate of the Hirasaka family to protect a barrier underneath Tokyo that separates the human world from the demons of another world. One day, an incident in the underground tunnels claims the lives of 6 civilians and a Hirasaka. The mass death and the mysterious circumstances under which it occurred have been hushed up by some powerful, but unknown, people. These people seem to be dismantling the barrier the Hirasaka family has fought so hard to protect, and it is up to the remaining Hirasaka to stop them.

From Anime News Network:

The story revolves around an underground barrier beneath Tokyo that separates our world from the evil spirits of another world. For centuries, the Hirasaka family has been entrusted with protecting this barrier. Within the past ten years, a conspiracy of unknown parties has been dismantling the barrier, piece by piece, and the future of Tokyo rests in one man who vows vengeance.