Akai Sato no Tengu

Akai Sato no Tengu (朱い里の天狗) is a one-shot manga by Magi Nagaha. It was serialized in Gangan Online.

Plot
Every ten years, a young woman is offered as a sacrifice to the mountain god. When the tengu goes to see the sacrifice, he finds out that the sacrifice actually volunteered for the role. And the sacrifice turns out to be a young…. boy.