From the 1984 chapter in the 4th edition of Phoenix:
Epoch didn’t have any competition against the second console that it released in Japan in 1984. The Game Pocket Computer was a handheld device similar to Milton Bradley’s pioneering Microvision. Despite the term handheld, the Game Pocket Computer needed two hands to operate it. The size of a small book, the console was 8.5 inches wide and nearly six inches vertically. Positioned almost in the center of the unit was a 75 x 64 pixel black & white LCD screen, which gave the console far greater resolution than the 16 x 16 screen that the Microvision provided.
The Game Pocket Computer was the first handheld unit in Japan. Like the Microvision, it was programmable by changing game cartridges. Unfortunately, the system was a failure and disappeared from store shelves not long after it was released. It is unclear why the system failed since stand-alone handheld, and programmable consoles, were popular. The reason might have been because there wasn’t any available software that made people rush out and buy a unit. In addition to a built-in puzzle game and drawing application, only five game cartridges were offered. It would be another five years until another hand-held console would be available. And that one would have a killer application.