The Japan World Exposition Association (hereinafter called the "Association") selected Mr. Taro Okamoto – a painter, sculptor, and critic – as the thematic exhibition producer. The reasons for adopting a producer system were that due to the characteristics of the tasks involved in them, it was difficult for the secretariat of the Association itself to create thematic exhibits, particularly in terms of concretizing the contents of such exhibits, and that even if the contents of the exhibition plan were to be publicly solicited, similar problems could emerge during their production process and it was thought to be impossible timewise.
Therefore, in order to effectively move forward with the tasks of creating thematic exhibits, the Association decided to entrust Mr. Okamoto with these tasks as the producer of thematic exhibitions and to conduct all tasks – from the design of the exhibition plan to the preparation, rendering, and direction of exhibitions – under such a system and under the management of the Association. Mr. Okamoto was appointed as producer on July 7, 1967 (Showa Year 42). He was chosen for the position from among many candidates, not just because Mr. Seiji Kaya, the chair of the Theme Committee, and Mr. Takeo Kuwabara, the vice-chair of the Committee, had recommended him for the role but also because Mr. Okamoto's unique ideas, his innovative originality, his powerful compositional skills, the richness of his artistic expressions, and his vitality were highly evaluated. He was assigned the job particularly because of his notable experiences and achievements, such as the production of a set of paintings Hi no Kabe (the Wall of the Sun) and Tsuki no Kabe (the Wall of the Moon) completed on 11 wall surfaces of the Tokyo Metropolitan Government Building in collaboration with Mr. Kenzo Tange, who was a professor at the University of Tokyo and served as producer of main facilities at the Expo – for which he had won the "International Grand Award for Architectural Painting" in France in 1959 (Showa Year 34).

The overall idea of the fundamental plan was that the Theme Pavilion was to be constructed as a complex consisting of three different, independent spaces. It meant that three spaces – the underground for the past, the ground for the present, and the mid-air for the future – would organically resonate with one another while existing independently and express one magnificent vision of the universe together. This idea was related to the mandala, the Oriental concept of the universe, and the philosophical and artistic spatial composition of the entire Theme Pavilion described in the plan was to be a symbol of Expo '70 together with the Tower of the Sun Museum.

The Theme Pavilion was divided into three exhibition spaces as follows:
Underground space – This "World of the Past and Origins" expresses the fundamental energies of all things in the universe that generate and run through the past, present, and future.
Ground space – This "World of the Present and Harmony" is lined with the three towers –　the Tower of the Sun Museum, the Tower of Youth, and the Tower of the Mother. The "Tree of Life," which symbolizes life forces that spew from their sources underground and flow toward the future, is contained inside the Tower of the Sun Museum. The history of life that has been ceaselessly passed down from generation to generation is represented in this space.
Mid-air space – This "World of the Future and Progress," built inside the "Big Roof," depicts the architecture and city plan of the future connected with the universe, humans, and their everyday lives.

This fundamental plan of thematic exhibitions was submitted by Producer Okamoto to the 9th Theme Committee Meeting held in Osaka on March 27, 1968 (Showa Year 43). Since there were worries that this plan could be a little too difficult to understand, the Association decided that it would listen to other people's opinions regarding the plan by conducting public hearings on April 12 in Tokyo and on April 13 in Osaka, to which about a dozen individuals of different ages employed in different occupations were invited. After these hearings, the fundamental plan was presented at the 10th Theme Committee Meeting held at the Science Museum, Tokyo on April 18 of the same year, and then was officially approved at the 30th Executive Committee Meeting on April 19.

After the approval of the plan, in order to proceed to the process of considering the detailed content of exhibitions and fleshing out the plan, Producer Okamoto selected four sub-producers from the scholars, architects, musicians, and designers working on the front lines of their fields – Mr. Shigeomi Hirano (Operations Management), Mr. Kazuhiko Chiba (Ground Space), Mr. Noboru Kawazoe (Mid-Air Space), and Mr. Sakyo Komatsu (Underground Space) – as well as a few other staff members, including Mr. Susumu Okada and Mr. Toshiro Mayuzumi, and advisors. In addition, he requested several other scholars and cultured people to provide their ideas.