In the late Edo era, Japan faced an unparalleled crisis caused by Kurofune (Black Ships), foreign ships. However, a massive robot known as Onigami, which has existed since ancient times, dispersed the Kurofune ships, completing the exclusion of outsiders. The narrative opens in Japan, where the Meiji restoration of 1868 did not take place. "I can be the greatest guy in the world because I am a virgin!" states the slogan.