12 years ago, Ultraman Tregear incapacitated the New Generation Heroes after misleading them to a minefield asteroid. Inheriting their powers, the Tri-Squad attempted to continue the battle but it leads to their particles scattered in outer space. Ultraman Taiga's particle of light merged with a young boy named Hiroyuki to save him from a fall after his Guesra companion "Chibisuke" was kidnapped. In the present day, Hiroyuki joined a private security organization E.G.I.S. (Enterprise of Guard and Investigation Services) to handle extraterrestrial cases while living in a society mixed with aliens from various point of origin. While handling a Villain Guild-related case, a fully recuperated Taiga awakens and therefore allows Hiroyuki to transform in order to combat giant monsters as two other Tri-Squad members, Titas and Fuma made their way to Earth and bonded with the former as a shared host.