Shin'ichi Chûjô was a scientist and linguist whose specialty was in the field of anthropology. He lived in the town of Karuizawa in the Kitasaku District of Nagano Prefecture in Japan. In 1961, the Japanese government and the nation of Rolisica sponsored an expedition to Infant Island to study the effects of radiation on some of the marooned survivors of the shipwrecked vessel, the Daini-Gen'you-Maru. Doctor Chûjô was one of the members of the team. Chûjô was familiar with the cultures of the island's primitive inhabitants, as well as those of neighboring islands. He was the first to interpret the symbology of a crucifix star hieroglyph found on the island, which he translated as "Mothra."
While exploring the island, Chujo passed through a cave and discovered the native juice came from mutant mold before he was attacked by a Vampire Plant. He was saved by the presence of two female fairies that were only twelve-inches tall. These "small beauties" came to be known as the Shobijin.
Back on the mainland, Chûjô discovered that members of the expedition had returned to the island and kidnapped the Shobijin, hoping to exploit them. Chujo and some others met with the Shobijin, who warned them that their island goddess, Mothra, has been angered and that good people may be hurt as a consequence of the actions of others.
The man who had kidnapped the Shobijin, Clark Nelson, fled to Rolisica with them, but Mothra, pursued them ultimately leading to a shootout between Clark and local law enforcement, which resulted in Nelson's demise. Chujo and the others went to Rolisica as well and recovered the Shobijin, then constructed a giant version of the Mothra symbol on an airport runway, which caused Mothra to land there. The Shobijin were reunited with Mothra and thanked Chujo and the others for helping them.
Forty-three years later, Doctor Chûjô was visited by his nephew Yoshito and his grandson Syun at his home, when the Shobijin suddenly appeared and greeted him. They revealed that they had come to seek help and believed that he was a man that could be trusted. The Shobijin told Chûjô that using Godzilla's bones to create the anti-monster robot Kiryu was considered blasphemous and that Kiryu had to be dismantled and Godzilla's bones returned to the sea. If not, Japan would once again become a target for Mothra's anger. The Shobijin plead with Chûjô to tell the Japanese government to shut down the project. Chûjô met with Prime Minister Hayato Igarashi and told him what the Shobijin had said. Igarashi apologized to Chûjô, stating that too much had already been invested in the project and that it was their only defense against Godzilla.
When Godzilla came ashore in Tokyo, Chûjô's daughter informed him that Syun was missing. Chûjô raced through the abandoned streets of Tokyo and found his grandson assembling desks in front of a school building. Chûjô asked Syun what he was doing, and discovered that he was constructing the Mothra symbol. Soon, Mothra flew over the city to do battle with Godzilla. While Chûjô and Syun tried to get to safety, a nearby building was damaged in the battle, causing rubble to fall near Syun. Chûjô pushed Syun out of the way and was buried under the rubble. Yoshito, a lead mechanic on the Kiryu project, had been relieved of duty so he could find his family, and discovered his uncle and cousin unconscious on the street. Yoshito brought them to a medical tent in the outskirts of the city, and thankfully both were fine and received only minor injuries.
- In both appearances, Chûjô was portrayed by actor Hiroshi Koizumi. Koizumi's reprisal of the role in Godzilla: Tokyo S.O.S. was the actor's final film role.