On November 22, 2010, Japan endured missile strikes in an incident labeled "Careless Monday," which fortunately caused no casualties. Society soon returned to its routine, leaving the event largely forgotten. Three months later, during her graduation trip to the United States, cheerful college student Saki Morimi encounters Akira Takizawa, who rescues her from a precarious situation. Takizawa appears eccentric; he is completely naked, suffers from amnesia, and believes he is a terrorist. Furthermore, he carries a peculiar cell phone containing 8.2 billion yen in digital currency. Although his behavior is highly suspicious, Saki forms a bond with the mysterious young man. Unaware of the truth, she is drawn into a thrilling death game centered on money, mobile devices, and the fate of the world. Higashi no Eden follows Saki as she attempts to decipher the secrets behind her rescuer, while Takizawa competes against other contenders equipped with similar phones, recovering memories that hint at his involvement in the earlier missile attacks.