After the terrifying invasion of kaiju in Japan, the government takes drastic measures by instituting the S-Class Species Suppression Protocol (SSSP). This initiative is aimed at tackling and eliminating any potential threats posed by these monstrous beings. In a gripping sequence of events, the SSSP responds to an alarming attack from an S-Class kaiju known as Neronga. Just then, a dazzling silver giant from beyond the stars descends upon the scene and swiftly vanquishes Neronga. However, this heroic act comes at a cost; Shinji Kaminaga, played by Takumi Saitô, suffers injuries while heroically rescuing a lost child amidst the chaos.
In the wake of this incident, Hiroko Asami, performed by Masami Nagasawa, joins the SSSP, transferring from her position at the Public Security Intelligence Agency and teaming up with the recovering Kaminaga. Asami initiates a report on the enigmatic silver giant, assigning it the moniker Ultraman. The SSSP quickly finds itself embroiled in another crisis when an S-Class kaiju called Gabora emerges. Unbeknownst to the SSSP personnel, Kaminaga has the ability to transform into Ultraman, now clad in striking red and silver colors. As Ultraman, Kaminaga successfully defeats Gabora, preventing a calamitous disaster at a nuclear waste facility.
Things take a darker turn when another extraterrestrial entity, known as Zarab, reaches out to the SSSP with the intent of establishing a treaty with Japan’s government. However, as Kaminaga unearths Zarab's ulterior motives—which involve inciting nations to war and destruction—Zarab's allegiance becomes questionable. In a shocking twist, Kaminaga finds himself captured and subdued by Zarab. In an effort to undermine Ultraman’s reputation, Zarab attacks strategic locations in Japan while masquerading as the hero. Furthermore, he disseminates footage revealing Kaminaga's transformation, leading to an international hunt for him. Amidst this turmoil, Asami receives the Beta Capsule from Kaminaga for safekeeping.
Despite the looming danger, Asami bravely locates and frees Kaminaga in a daring rescue, although she is quickly captured by Zarab. In a moment of sheer determination, Kaminaga retrieves the Beta Capsule, transforms into Ultraman, saving Asami once more and dismantling Zarab’s deceit by exposing his true form before ultimately defeating him.
However, the plot thickens when another alien, Mefilas, abducts Asami and forcibly transforms her into a giant under his mind control. In an act of twisted generosity, Mefilas reverses this transformation using the Beta Box—a large-scale version of the Beta Capsule. He seeks to strike a deal with the Japanese government, offering the Beta Box for their strategic usage, under the condition of absolute obedience. Kaminaga, vehemently opposed to Mefilas' plan, secretly collaborates with the SSSP to halt this dangerous agreement. Together, they craftily intercept the Beta Box, leading to a thrilling showdown between Ultraman and Mefilas. The tables turn when Mefilas, realizing Ultraman is under the watchful gaze of the superior Zōffy, abandons his plans, warning Ultraman about an impending threat before making his exit from Earth with the Beta Box.
Following these events, the SSSP faces a temporary detainment for their allegiance to Ultraman but are swiftly exonerated after their Chief skillfully persuades his higher-ups of the truth. A vital conversation occurs when Kaminaga meets Zōffy in a serene forest—the very place where he sustained his injuries. It is revealed that Kaminaga did not merely get hurt; he was actually killed by debris upon Ultraman's descent. Understanding the gravity of his sacrifice, Ultraman chose to adopt Kaminaga’s identity to comprehend the human experience. Zōffy informs Ultraman that he faces impending repercussions for breaching their celestial laws regarding union with a human form. Zōffy, convinced of the threat humanity poses if allowed to ascend in power, unleashes Zetton—the ultimate weapon engineered to annihilate them.
Kaminaga’s determination shines through as he alerts the SSSP to this development, providing them with critical intel on a flash drive before he launches into orbit as Ultraman to intercept Zetton. Despite his valiant efforts, Kaminaga finds himself outmatched and is ultimately hospitalized. In a heart-wrenching decision, the government resolves to conceal humanity's fate as a final act of kindness. Meanwhile, Akihisa Taki, portrayed by Daiki Arioka, a physicist within the SSSP, enthusiastically investigates Kaminaga's flash drive, uncovering revolutionary concepts regarding the Beta Capsule and dimensional theory.
Once Kaminaga awakens, Taki reveals not only the insights hidden within the drive but also a collaborative plan between him and renowned scientists from different nations to neutralize Zetton. Donning the mantle of Ultraman once more, Kaminaga activates the Beta Capsule and opens a black hole just before Zetton unleashes its devastating heatwave. The black hole devours both Zetton and Ultraman, but Zōffy miraculously saves Ultraman in the nick of time.
Zōffy, insisting that Ultraman return to their world, finds himself at odds with Ultraman's wish to guard Earth. Their philosophical clash intensifies, ultimately leading Ultraman to make the ultimate sacrifice: to resurrect Kaminaga. Zōffy queries Ultraman's intent to sacrifice himself for what he perceives as an inferior race, yet, upon witnessing the indomitable spirit of humanity in their relentless striving against destruction, Zōffy's perspective begins to shift. The story reaches a poignant conclusion as the SSSP welcomes Kaminaga back to life, witnessing his triumphant awakening and second chance.
