Hirayu is the oldest and most famous hot spring in the Okuhida hot spring area. The origin of Hirayu began when Takeda Shingen attacked Hida. The general is Yamagata Masakage. He led a large force and got over the pass, but they were troubled by the mist of the rugged mountain pass. When the forces of Singen arrived near Hirayu, a old white monkcy appeared before them. The monkey told them that a hot spring was in their neighborhood. Shingen's forces had a bath at the hot springs to recover from the fatigue of their journey.