"This year's sacrifice is you." With those words, Guest's life came to an end. In this village, known as the 'Home of the Serpent God,' the custom of offering a sacrifice to the mountain's serpent deity has continued for hundreds of years. The sacrifice never returns. They are devoured to the bone by the Serpent God, their soul imprisoned in the mountains forever. Having heard this legend since childhood, Guest never thought to doubt it. That was why they didn't think of running away. To protect the village, to protect their family. Because they believed that was the duty of the one chosen as the sacrifice.

The day of the ritual. Dressed in white robes, Guest heads alone toward the shrine deep in the dim mountains. With every step up the mountain, the sound of drums behind fades further away. Eventually, only silence remains. Reaching an old stone tunnel, passing through it leads to the Serpent God's shrine. There's no one here... or so they thought, until—