In Victorian-era London, on the night of Ciel Phantomhive's tenth birthday a fire destroyed his manor and killed both of his parents. In a moment of death Ceil strikes a deal with a demon, his soul in exchange for revenge. This demon becomes his butler and calls himself by name of Sebastian Michaelis, to protect and serve Ciel until the deal has been completed. One month after the fire Ciel returns from being missing, with his new butler Sebastian. Ceil is now the head of the Phantomhive corporation, handling all business affairs as well as the work as the Queen of England’s guard dog and looking for his parents murders.
Set in the year 2039, Japan is the under the rule of a multinational military force called GHQ after the country went into chaos due to the "Lost Christmas" incident ten years prior to the start of the series, when a giant outbreak of an alien virus called the Apocalypse Virus spreads during Christmas, causing the United Nations to send the GHQ to contain the outbreak and restore order. The series follows Shu Ouma, an intelligent yet socially awkward teenager who finds himself caught in the war between the GHQ and "Funeral Parlor (Undertakers)", a resistance organization led by Gai Tsutsugami, which aims to liberate Japan from the GHQ, when he meets Inori Yuzuriha, the famous Internet Singer of the band Egoist and a member of the Undertakers. Due to various circumstances, Shu acquires a genetic weapon called the Void Genome, also known as "power of kings", which allows him to extract "Voids", objects with special properties that reflect the personality of their owners from underage individuals. With his new powers, Shu joins the Undertakers to protect Inori and learns secrets and mysteries he never knew.