Traveling in search of the rare ingredient, “sky fish” Meliodas and Hawk arrive at a palace that floats above the clouds. The people there are busy preparing a ceremony, meant to protect their home from a ferocious beast that awakens once every 3,000 years. But before the ritual is complete, the Six Knights of Black—a Demon Clan army—removes the seal on the beast, threatening the lives of everyone in the Sky Palace.

Earth has regained peace, but a new enemy with space-time powers has arrived! Musashi, Cosmos' host, tells the UPG that the Ultra Warriors have been sealed inside an evil space-time castle by a warrior woman named Arina. The fate of the entire world will be at stake. Hikaru and Shou are not strong enough to face this enemy, but if they can learn to fuse their hearts, they stand a chance. But to do that, they first must survive the training of Ultraman Zero!

The anime's story is set in 2027, one year after the end of the fourth non-nuclear war. New Port City is still reeling from the war's aftermath when it suffers a bombing caused by a self-propelled mine. Then, a military member implicated in arms-dealing bribes is gunned down. During the investigation, Public Security Section's Daisuke Aramaki encounters Motoko Kusanagi, the cyborg wizard-level hacker assigned to the military's 501st Secret Unit. Batou, a man with the "eye that does not sleep," suspects that Kusanagi is the one behind the bombing. The Niihama Prefectural Police detective Togusa is pursuing his own dual cases of the shooting death and a prostitute's murder. Motoko herself is being watched by the 501st Secret Unit's head Kurutsu and cyborg agents. Written by Jiilo_Kim