Chikyuu Kaihou Gun ZAS is a vertically scrolling shoot-'em-up, released on December 18, 1992 by T&E Soft, Inc. Only released in Japan, the title translates roughly to "Earth Liberation Army." Since the game's release, it has seen minimal coverage and sparse reviews, although those that have reviewed it are positive in regards to ZAS, due to its detailed graphics, varied gameplay, and multi-level scrolling backgrounds.
The graphics in Chikyuu Kaihou Gun ZAS are fairly unique in terms of "Game Boy space shooters." The game uses the Game Boy's screen blurriness to its advantage, creating effects such as a scrolling background and transparency. This makes the game slightly difficult to play on an emulator or Super Game Boy, as these effects are translated to flickering sprites rather than the smoothness that would be seen on an original Game Boy.
ZAS is extremely similar to R-Type in terms of gameplay. ZAS contains five stages; a mixture of tight enclosures akin to R-Type, and open air battles. Each stage is littered with enemies, obstacles, and power-ups, and each level has a boss at the end that must be faced before the player can progress to the next level. Power-ups include a variety of objects, such as extra ships, extra lives, better lasers, and shielding.
After completing all five of the game's levels, players are presented with an ending cinematic which depicts the player's ship flying back to Earth.