The story follows a player-named protagonist who lives in near-future Tokyo. When a portal to the realm of demons is opened accidentally by a scientist named Steven and is seized by Gotou, a military commander who believes that he can control the demons, the United States government orders a nuclear attack on Tokyo. Transported with two other supporting characters thirty years into the future, the protagonist finds the Earth ruined by a demon invasion, which is now the stage for an escalating conflict between the Order of Messiah and the Ring of Gaia, conflicting cults who wish to bring about kingdoms for their respective patron deities (YHVH and Lucifer). The story is influenced by moral decisions the protagonist makes, aligning him either with the Messians, the Ring of Gaia, or setting him up as an independent agent.