After once being a terrifying Demon Lord in Ente Isla, Sadao Maou now lives a peaceful life in Tokyo, having been defeated by the hero Emilia Justinia and escaping to Earth. He works as a humble fast-food restaurant employee while also caring for his former generals, Alciel and Lucifer, who have followed him to Japan. However, he must remain wary of Emi Yusa (alias Emilia) and the angels who monitor his actions. During a heated argument between Sadao and Emi, a strange dimensional portal suddenly appears, revealing an apple cradling a young child named Alas Ramus. Surprisingly, the child quickly becomes attached to both Emi and Sadao, considering them both her parents. Though Emi initially hesitates, she eventually agrees to help Sadao in raising Alas Ramus. However, their idyllic life is abruptly shattered when archangel Gabriel arrives with shocking news. He claims that both Alas Ramus and Emi's holy sword must be taken to prevent the world's destruction. Despite their past animosity, Sadao and Emi put aside their differences to protect those they love and reject Gabriel's ominous warning.