The Otafuku mask doesn't appear in any Iwami kagura dances that I know of, but it is worn by the female half of a kyogen duo. Otafuku is commonly known as the "goddess of mirth", and also goes by the name of Okame. It is believed that the mask is developed from the Uzume mask. The motif of the Otafuku mask is a common design found all over the place, but not often talked about is the sexual side of her nature.
I found this pair of huge masks gracing the entrance to a large shrine in Shikoku. I have seen her paired with a tengu before, and I've read about a performance at a fertility shrine in Asuka involving a tengu and an otafuku that is overtly sexual. The tengu/red demon most probably is derived from Uzume's husband, Sarutahiko, a giant being that has a very large nose.
My favorite derivation of the Otafuku mask though is this little sculpture I found at a fertility shrine in Yamaguchi.
Iwami Kagura Mask index