Under the planning of Hannah and others, Charles Phantomhive has broken away from his human identity and become a demon. As his deacon during his lifetime, Sebastian Michaelis was forever bound by him and existed as a demon deacon forever.
After that, the bored Ciel took back the title of "Queen's Watchdog" and continued his "life". However, a strange girl appeared in a case, which made Ciel, a devil, discover that the devil's ability is so small.
"Hey, Sebas, expose that woman's true identity. This is an order."
"Yes, my lord."
The familiar voice sounded again. Let us wait and see. Facing powerful forces, can the perfect deacon still serve his master perfectly?