Kenkokukai/National Foundation Society (a.k.a. State Foundation Society, a.k.a. The Society to Build the Country) was an ultranationalist organization for "the creation of a genuine people's state based on unanimity between the people and the emperor".
Source.
Another useful excerpt...
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kenkokukai badgenationalfoundation day badgenationalfoundationsocietybadgenationalfoundationsocietymembershipbadge
建国会徽章
建国祭記念章
建國會會員章
建國祭之章