Childhood Names (幼名)
The term "childhood name" (yomyo or yomei in Japanese) refers to a name for use by someone only in his childhood (this custom was more or less limited to male children). Osanana and shoji are two other terms that can be used to describe this same type of childhood name.
Such childhood names were in use primarily from the Heian through to the Edo periods for the children of military or noble families during their childhoods, and most often ceased to be used once the child passed through the coming of age ceremony and received his imina (real name) for adulthood. The names of members of the peasant class were also called "yomyo" (childhood names), but unlike the children of the upper class, they did not receive an imina at adulthood.
The custom of passing on and inheriting yomyo
Many military families adopted the tradition of passing childhood names down generation to generation. Examples abound: the name the Shogunal branch of the Tokugawa family passed down was Takechiyo, while that of the Owari branch of the Tokugawa family was Gorota, that of the Kishu branch (in Kii Province) of the Tokugawa family Chofukumaru, that for the Mito branch of the Tokugawa family Tsuruchiyo, and that of the Maeda clan Inuchiyo, as well as countless others. Each such name had originally been the childhood name of the founder of the family (so for example, the name Takechiyo had been the first Edo-period Shogun, Ieyasu TOKUGAWA's name, while Gorota had been the Owari branch progenitor Yoshinao TOKUGAWA's, Chofukumaru the Kishu branch founder Yorinobu TOKUGAWA's, Tsuruchiyo the Mito branch forefather Yorifusa TOKUGAWA's, and Inuchiyo the Kaga Domain patriarch Toshiie MAEDA's), and each was passed down from family head to the son being groomed as heir, becoming their childhood name in turn; this passing down continued from generation to generation.
List of childhood names passed down from generation to generation among military families
The Hosokawa clan - Someimaru
The Ouchi clan - Kidomaru
The Shogunal (i.e., main) branch of the Tokugawa family - Takechiyo
The Owari branch of the Tokugawa family - Gorota
The Kishu branch of the Tokugawa family - Chofukumaru
The Mito branch of the Tokugawa family - Tsuruchiyo
The Maeda clan - Inuchiyo
List of childhood names of famous historical figures
MINAMOTO no Yoshiie - Fudomaru
MINAMOTO no Yoritomo - Onimusha
MINAMOTO no Yoshitsune - Ushiwakamaru
MINAMOTO no Yoshinaka - Komaomaru
Tokimune HOJO - Seijumaru
Masashige KUSUNOKI - Tamonmaru
Takauji ASHIKAGA - Matataro
Yoshiakira ASHIKAGA - Senjuo
Katsumoto HOSOKAWA - Someimaru
Motonari MORI - Shojumaru
Nobunaga ODA - Kipposhi
Hideyoshi TOYOTOMI - Hiyoshimaru
Toshiie MAEDA - Inuchiyo
Ieyasu TOKUGAWA - Takechiyo
Masamune DATE - Bontenmaru
Tomoshige KIMURA - Sukekuro