These two demon masks were located behind the main building of the Hachiman Shrine in Yuki, a fishing village on the south coast of Tokushima. The spot is named Oni no Koshikake, "Demons Seat".
Apparently several local people saw an Oni sitting at this spot. Interestingly this is not a story from long ago, as it happened on September 15th, 2002.
Being a Hachiman Shrine, the main kami is Ojin, his mother, Jingu, and either his father Chuai, or his "wife" Himegami.
There was a small Ebisu shrine in the grounds, not surprising at it is a fishing village.