The FC Demons are a pair of interactable NPCs found in the FC World. One of them is an Effect-giving NPC that gives Madotsuki the Demon Effect.
Overview
The first one can be encountered in FC World B. There is a 1-in-6 chance that they will appear in the place which has its entrance surrounded by six pyramids. However, they will always appear if Madotsuki has the Demon effect equipped. They teleport Madotsuki to the FC Basement, right next to the second FC Demon.
The second one can be found inside the FC Demon's Room in FC Basement. The Demon effect can be acquired by interacting with them. The FC Demon resembles a traditional Japanese Oni due to their red color and horns.