Demon Contract: a Millennium Agreement with the Nine-Tailed Fox

The human world and the monster world were originally isolated, but due to the "collapse of the pillar of heaven", the two worlds began to merge, and monsters hid in the market. The protagonist is an ordinary college student who rescues an injured white fox one night, but does not know that it is a demon princess. In order to repay his kindness, the white fox signed a "demon contract" with the protagonist to share life and strength. But once the demon contract is formed, enemies of the demon clan and demon hunters come to visit one after another. What's even more troublesome is that the protagonist discovers that the blood of the ancient "monster-suppressing master" flows in his body - he should be at odds with the demon clan!