Riku Asakura is a teenager with no knowledge of his past, save being found near an astronomical observatory as a baby following a universe-wide cataclysm called the Crisis Impact. When a giant monster destroys his home, Riku and his alien roommate Pega stumble upon a secret base 500 meters under Earth. Riku learns he is an Ultraman in human form and is given the ability to use the Geed Riser transformation device and Ultra Capsules by the base's operating system RE.M. to become Ultraman Geed to save everyone. But Riku later learns that he is the son of the instigator of the Crisis Impact: Ultraman Belial. Deciding to fight against fate, he is joined by monster hunter Laiha Toba, AIB agent Moa Aizaki, and office worker Leito Igaguri, who becomes the host of Belial's nemesis Ultraman Zero. Riku soon learns that the monsters he faces are Fusion Rise forms of Kei Fukuide, who seeks those who are hosts to unformed Ultra Capsules called Little Stars. In the middle of the series, Riku discovered that he was a clone of Belial manufactured by Kei to gather the Ultra Capsules in order to revive the dark Ultra. At some point of time, Belial returned to Earth and kidnapped his son in an attempt to sway the latter to his side but failed due to Ultraman King and Laiha's intervention. With the power bestowed by Ultraman King, Geed received a new form known as Royal Mega-Master and defeated his father. With Belial's seeming death, Kei try to succeed his master by following his footsteps but found himself abandoned by Belial, who in fact recuperated within nonfiction writer Arie Ishikari and stole the former's Sturm Organ. Along with assuming the form known as Atrocious, Belial tries to absorb Ultraman King's essence, destroying Earth and moved on to attack the Land of Light and his inhabitants. Zero succeeded in separating Ultraman King from Belial while Father of Ultra came to Earth and sealed him within a barrier. The next day, Riku took matters on his own as he fights his father in one-on-one combat with his will allowing Ultraman King to summon copies of his Fusion Rise forms into his aid. Near the end of the fight, Riku tried to understand his father's pain and suffering from his banishment but was forced to kill when Belial is beyond reasoning. With the fight over, a fully healed Zero joined Father of Ultra and Ultraman King as they left Earth and Riku resumed his normal life.
Ultraman Geed made his debut in the final scene of Ultra Fight Orb, where he was shown killing Reibatos when other Ultras assumed him to have died after being defeated by Ultraman Orb, though this is proven to be non-canon as shown in the series finale in which Belial was the one who killed Reibatos.
The Ultraman Geed trademark was filed by Tsuburaya Productions on March 6, 2017. The series was announced on April 27, 2017 by the official website of Tsuburaya Productions and Sports Hochi. The main actor Tatsuomi Hamada mentioned that becoming an Ultraman is a childhood dream since his kindergarten. As he had once played Nao, one of the protagonists in the 2010 Ultra Series movie , he is also excited to view Belial as a father instead of an antagonist of the previous movie while his character grew up and faced his destiny. According to Koichi Sakamoto, he views Riku as a man who fights as Belial's son while facing challenges without getting bound by the "common senses of an Ultraman series". As the show revolves around a protagonist fighting with the blood of a villain, he related the plot towards that of Devilman. Writer Otsuichi mentioned that he used to watch Ultraman X and Ultraman Orb with his son back home and was advised to use Arthur C. Clarke's novel Childhood's End as a reference material for the first stage of the project. Said author's name becomes the foundation of the main character's name, Riku Asakura. The theme of Riku being Belial's son was an idea he thought of but never expected it to be conceptualized by Tsuburaya themselves. He stresses the difficulty of writing the script of the first episode, with the Ultra and the transformation item that were yet to be named. He is also well-aware that this is not the first tokusatsu series to be written by a novelist, as this was preceded by Gen Urobuchi in Kamen Rider Gaim.
