For thousands of years, the oni has played a large role in Japanese culture. Similar to a troll or bogeyman, oni do not always represent evil. While some feast on humans, (look at those sharp teeth), others are friendly and will help humans with whatever they need. When you wear the Oni Blue Demon Mask, you have a choice to make between good and evil. The full-face mask is a bright shade of blue and features two horns on either side of the head, large eyes, and sharp fangs. Eye slits above the head allow limited vision.