The story is set in a world where a tokusatsu hero TV series "Outer Man" has gained national popularity for 50 years (just like the Ultraman series). One day, a giant alien looking exactly like Outer Man appears in Japan. The truth is soon revealed that, unlike the story in the TV series, Outer Man is an evil alien who has been trying to brainwash Japanese people to invade the earth. The actors who played the hero in the TV series decide to fight against the real Outer Man by transforming into the villain alien in the series, Sylvie Seijin.
Eight years after saving the SPD from Agent Abrella's scheme, the Dekarangers parted ways with Ban joining the Fire Squad, Jasmine marrying Hikaru Hiwatari, and Swan working independently while Tetsu, Hoji, Sen, and Umeko continue working under Doggie Kruger. But after an incident occurred that hospitalized Kruger on planet Revaful wherein he was labeled as a dirty cop for an apparent dealing with the Qurlian Crime Family, which went awry with the death of a civilian witness, Tetsu takes over the Earth Branch. Two years later, joined by rookie officers Assam Asimov and Mugi Grafton, who had taken over the positions of Deka Red and Deka Yellow respectively, Hoji, Sen and Umeko encounter a Clementian named Carrie who is being hunted by Mechanoids.
Kota Mizutani, a 10-year-old boy whose health worsened after he saw a murder, is brought to Akiko's clinic by his mother Mariko. Kota says that two months ago, he witnessed a man in a park strangling a woman with a cord and was chased by the man afterwards. Hamada, who listens to his story along with Akiko, immediately performs an investigation but cannot find any traces of the crime. However, Kota's testimony gains credence when the body of a woman killed two months before is discovered on a construction site in Kawagoe. Acting on a tip from a citizen who says she had been wearing the same clothes as the victim, the police search the house of Kazuko Shimazaki, a photographer who is often absent. But when Kazuko returns from her trip with her assistant Hirano, it becomes clear the victim is a different person.
