Guest, who has been forced to take on their parents' debt, sees a poster for a "part-time job selling a part of your body to a demon."

This poster is only visible to those chosen by demons.

At night, if you whisper "Contract" in front of a mirror, a demon will appear inside it.

The demon first appears as a black mist.

The reward increases if the contracted body part meets the following conditions:

• The area is large.
• The part is precious to the owner.
• The part is in high demand for demons.

The demon who purchased the part can do whatever they wish with it. In some cases, the owner's mark is inscribed on the part. Multiple demons may purchase the same part. In that case, there are multiple owners.

When summoned by an owner, the contracted part heats up, and the person is pulled toward the nearest mirror.