In October 2006, Hirameki International released an English edition of the Windows version in the United States.
The explanation for this name is a bit of a pun, as "yojinbo" itself means "bodyguards" in English, and three of the main characters have nicknames that make up this phrase (Yo, Jin, and Bo).
She finds a mysterious pendant while out helping with an archeological dig (she's in the high school history club, so she is forced to attend), and later has a strange dream—it seems that the scene is from about a hundred and fifty years ago, during the last days of the samurai, and she sees Hatsuhime, princess of the Mochizuke clan, assassinated!
It gets even more strange when the scene changes, and Sayori realizes that she's in Hatsuhime's body; that she has somehow seen how things were, and the situation has somehow "reset", giving her the chance to avert the princess's terrible fate.
The atmosphere is similar to the anime series Cowboy Bebop and Samurai Champloo, due to all the anachronisms and references to aspects of popular culture.