Kokuiko was also used in Japan during the Pacific War for its idea of protecting the 'unbroken line of sovereignty in the hands of Emperors' as well as by being understood as the source of the 'reverence for the Emperor.'
太平洋戦争中の日本では、「万世一系の国体」を擁護する思想や「尊皇精神」の源流として理解され、利用された書でもある。