A long time ago, a pair of twins were born. Back then, however, multiple births were considered unlucky, so one of the twins, a girl, was... crushed to death with a millstone, buried under the shade of a large mulberry tree. The girl's soul, lacking a fully grown spirit, could not reincarnate, and as such was forced to wander the world. Only after collecting 108 individual sources of human misery/worldly desire could she move onto the next world.