Ultraman Decker takes place years after the end of Ultraman Trigger: New Generation Tiga, where Earth has entered a period of peace once again. When humanity begins their outer space exploration program and their monster attack countermeasures diminish at the same time, the Spheres launch their attacks, causing Earth to be desolated and become a lone star. A civilian named Kanata Asumi bonds with the titular Ultraman Decker and joins the newly reformed GUTS-Select in addition to his fellow rookie members in their fight against the Spheres.
