Ganbare Goemon: Tengu-tō no Gyakushū! is a Ganbare Goemon game released for the Game Boy Color on January 14, 1999. Unlike most games in the series, this game is actually an role-playing game, a genre which was used first in the Ganbare Goemon Gaiden games for the Famicom. The game also borrows some concepts from the franchise's anime series.
The main protagonist in the game is a boy named Hiroshi, who somehow gets transported into a Ganbare Goemon game and teams with Goemon in order to save Japan from some evil force.
Source: Wikipedia, "Ganbare Goemon: Tengu-tō no Gyakushū!", available under the CC-BY-SA License.