It is in this new age when "Sphere," an invading swarm of mysterious floating space objects, begin to attack Earth. Humanity loses contact with space and becomes a lone star. Their attack throws our hero Kanata Asumi's peaceful life into chaos. Destruction spreads before his eyes and a giant monster appears. With no heed for his own safety, Kanata jumps in front of the enemy and transforms into Ultraman Decker.
