From MangaHelpers:

The world is filled with many strange events, from the horrific to the more exciting. But one city was “visited” by a single “egg” that held an unknown “demon,” which was investigated by the many people of the world. Humans who have come in relation to those connected to the “egg” ended up dying out of pain and suffering. To end this havoc of suffering, the one existence directly related to the egg, the Dog-Lord, and a German lady who has transferred to the country for yet unexplained reasons, are the only ones who can do something to this “egg,” but what is this egg exactly? Was the one who came out of the egg really the demon they think it is? [Midori-Mori]