On November 22, 2010, Japan was struck by missile attacks, a terrorist act that, fortunately, caused no injuries and became known as "Careless Monday." Quickly forgotten, society continues with its daily life as usual. Three months later, during her graduation trip to America, the life of friendly college student Saki Morimi is permanently altered when she is rescued from unexpected trouble by Akira Takizawa. Takizawa is cheerful yet peculiar in many respects—he is completely naked and suffers from amnesia, believing himself to be a terrorist. Furthermore, he possesses a strange cell phone loaded with 8.2 billion yen in digital cash. Despite Takizawa's suspicious characteristics, Saki quickly befriends the enigmatic young man. However, unknown to her, this marks the start of a thrilling death game involving money, cell phones, and the salvation of the world. Higashi no Eden chronicles Saki's struggle to unravel the mysteries surrounding her savior, while Takizawa himself battles other individuals armed with similar cell phones and recovering memories that reveal his possible connection to the event from months ago.