15-year-old Love Heartbreaker is a homeless orphan who accidentally stumbles upon a secret military base. Inside he finds a top-secret portal that leads to an apocalyptic world full of advanced undead and underground bunkers. A world he now has become trapped inside. Finding him on the surface, the military quickly moves him to an underground city where he finds himself going to an underground school. It is there that he truly uncovers the secrets that lie between the apocalyptic world and his own.