It was customary in the samurai society during the medieval ages to have someone special become a nominal father to perform the role of placing an eboshi on a boy's head at the family's request when the boy celebrates the genpuku ceremony. This nominal father was called the "eboshi-oya," and the young man, who was crowned with an eboshi, was called the "eboshi-go." At that time, the young man abandons his childhood name and a new name, called "eboshi-na," is given to him by the eboshi-oya.
There is mentioning in "Azuma Kagami" (Mirror of the East) that MINAMOTO no Yoritomo served as an eboshi-oya of Tomomitsu OYAMA, a son of SAMUKAWA-no-Ama, who was Yoritomo's wet nurse, on October 29, 1180. Likewise, lords, toryo (head of the clan), and trustworthy influential person were frequently asked to serve as eboshi-oya. The Kamakura bakufu defined that the relationship between eboshi-oya and eboshi-go is equal to that between real parent and child, even if the former has no blood relation. There were even laws passed in 1235, which prohibited not only relatives but also eboshi-go from attending council.
In genpuku ceremonies held after the Muromachi period, young men more frequently had their forelocks shaved instead of having an eboshi placed on their head. And it was the eboshi-oya's role to shave the young man's forelock. In addition to the samurai society, the court noble society during the Nara and Heian periods also had coming-of-age ceremonies where nominal parents, similar to the eboshi-oya, assumed the role of "hiki-ire" (a person who sets a young man's hair into a crown) during a Kanrei (a ceremony where a man is given a crown for his attainment of manhood) and "koshi-yui" (a person who ties a band around a young woman's waist for her coming-of-age ceremony) during a Mogi (coming-of-age ceremony for girls). The early-modern times also saw similar ceremonies in which nominal parents played the role of "master" in the "Oyakata-kogata-sei" (system of a master and disciples) and "kaneoya" (also called "fudeoya," a women who cares the first black-painting of teeth ceremony of a girl). These coming-of-age ceremonies managed by nominal parents still remain in some regions of Japan.