One morning, a wanderer, lost in the forest, came upon a stream deep in the forest. Hungry and exhausted, he thought of fetching a drink. He saw a young boy with blue hair appear at the base of a tree in the water. He looked at the wanderer with a curious gaze and said in a low voice: "Will you drink this water? ... If your heart is not pure, it will immediately become poison." This encounter was not only a meeting with the spirits who protect the forest, but also the beginning of a friendship and a test of the lost human heart.