There are no false notes in a score written in blood.

Brilliant neoclassical composer Amamiya Yasuo has learned a cruel lesson: human loyalty is a cheap counterfeit that breaks at the first sign of discomfort. His wife's betrayal forever destroyed his desire to trust mortals. But Yasuo is a pragmatist and a perfectionist. If devotion cannot be earned through sincerity, it must be bound by magic.

Turning to ancient demonology, Yasuo summons a creature from the Abyss. No compromises, no feelings—only a mathematically precise, ironclad contract that strips the demon of any right to escape. For the maestro, this union is a guarantee of absolute control, an eternal source of inspiration, and the perfect way to turn the life of his ex-wife, who still lives in his mansion, into elegant psychological torture.

But when a wounded, cynical genius and an immortal being bound by the seal of the underworld find themselves under the same roof, a dangerous intellectual game begins. Will the demon find a loophole in the maestro's flawless rules?