Torture Princess: Fremd Torturchen, Vol. 3 (light novel) — Keishi Ayasato

For that person's sake, I could do or become anything.
The Grand King, Fiore, has been defeated, but her death came at a great cost. Hina's critical condition has forced her into a deep sleep, and Kaito, desperate for power, has forged a contract with the Kaiser. When troubling news arrives from the Church, the situation grows dire. A new demonic presence has devastated the Capital. Godd Deos is dead. Elisabeth and Kaito rush to the scene to face the threat but are wholly unprepared for what they find...
The contractors of the final three demons-the Monarch, the Grand Monarch, and the King-have been fused together to create a living nightmare...