In ancient times, all of the demons recorded in the Classic of Mountains and Seas really existed. They absorbed humankind's thoughts to become more powerful. As time passed, people gradually forgot about their existence. The demons that were forgotten were all faced with the fate of disappearing...... there is a family that serves to guard and protect the only demon remaining in the world. As they painted and recorded, they were — the artists of the Classic of Mountains and Seas.

Source: http://www.u17.com/comic/81359.html