In the desolate streets of London—when ordinary people were returning home, or when the hidden spirits lurking inside someone's house were making the residents' lives miserable—there was one figure who moved silently through the darkness. Wrapped in a long black overcoat, this man destroyed those souls and sent them straight to Hell. He was none other than a Demon Slayer, sent to Earth by the Hell King, Lucifer. His name was Michael.
Along with Michael, a girl had also come to Earth. She was not only Michael's closest ally but also Lucifer's most trusted commander. Her name was Mercy. Yet her nature was the complete opposite of her name—there was no mercy in her at all. She showed no compassion toward the spirits; instead, she became utterly ruthless, slicing souls apart with the twin blades she carried, forged from the flames of Hell itself. After being cut by those infernal blades, the spirits could never go to Heaven or Hell again.
