A Chozu-bachi is a stone washbasin for a purification ceremony to clean up our bodies and souls before entering into sacred places. Such a washbasin is typically placed at the entrances of shrines, temples, tea houses, and various Japanese traditional gardens.
The strange shape of this Chozu-bachi seems to imply Yin-Yang stones, which is said to have been installed in every Daimyo-garden for praying for the eternal longevity and prosperity of the feudal clan and its descendants.
Daimyo lords incorporated the idea of Shenxian thought into the designs of their gardens. This philosophy is based on the ancient Chinese folk belief about the existence of Mount Penglai, which is the enchanted island of eternal youth and immortality.
The worship of Yin-Yang stones comes from this Shenxian thought which was a predominant world view of the Japanese in the Edo period.
Yin-Yang stones are the rocks in the shape of male and female genitalia in pairs, which promise us good fortune for marriage and safe delivery.
To Daimyo lords, the failure to produce their heirs meant the end of their clans and families, so they implicitly placed such stones in their gardens as a good luck charm for their longevity and prosperity.
Furthermore, evergreen pine-trees were planted extensively in Daimyo gardens as an auspicious symbol of everlasting happiness.
