Shirai Seiichi's education in the context of the interwar events influenced his path and molded him into a defender of idealism. Starting from the early evolution of his ideas, Shirai's significant concepts are outlined to show how they stood apart from and challenged the Japanese modernist debates over the architectural responses to war and industrialization. Examples of Shirai's early work along with surrounding historical events show how Shirai's perceptions of the use of space and its manifestation in architecture, based on Kantian ideas of a priori creation, contradicted orthodox modernist architectural theory and practice. Shirai's evolving theories and their impact on his design are introduced through his early training and related projects. However, it is his unrealized plan for the Genbakud? that is analyzed as primary evidence for the idea that Shirai was the only mid-twentieth century Japanese architect who could effectively express the sad destiny of the nuclear age. Last, specific examples of Shirai's mid to late career work to demonstrate how his conceptual framework evolved. Interviews, commentary, and theoretical analyses of his works show his unique trajectory and role in contrast to his modernist colleagues, and provide insight into Shirai's investigation into the universality and potential of the human spirit (fuhen no anima). Finally, recent discussion about constructing the Genbakud? based on Shirai's blueprints raise the idea that Shirai's early ideals are now ready to be presented in the post-modernist age.