During the course of the game, an alien invasion takes place, lead by cybernetic beings dubbed the Bio-Mecha (or Bio-Mechs). Gamera joins forces with the international organization called the Science Defense Academy against the invaders, who soon counterattack with the creation of the Neo-Gyaos; mutant variants of the 1995 creatures, of numerous shapes, sizes, and destructive capabilities.
The game contains several cut-scenes with real live actors. The game can be heard in English or in Japanese, with Japanese subtitles.
In the game, the player is part of the United Nations Military, who can loosely command Gamera to attack enemies, as well as having the power to attack with the player's ship's laser. Gamera is far more powerful, however.
The game plays somewhat like a rail-gun game, as most of the stages are relatively linear. The game travels through a variety of settings, such as cities, oceans, forests and caves.
With some exceptions (Gyaos Man, Quicksilver, M-Machine-Dread VII, Bionic Gyaos, etc), the majority of the game's original monsters' official names are unknown to American audiences. The following lists are mostly comprised of 'descriptive names', based on the characters' appearances and abilities.
Genetically engineered, custom built 'attack beasts' of the Bio-Mechs, created from the genes of 1995 Super Gyaos, which they had stolen from the Science Defense Academy. And with the final Neo-Gyaos monster, the colossal Bionic Gyaos (the Dragon Fortress) which is a threefold hybrid of Gyaos and Gamera DNA, along with Bio-Mech technology.
- Neo-Gyaos (Two-Headed Gyaos)
- Gyaos;Man (Kind)
- G;Bionic Gyaos (The Dragon Fortress)
- Gyaos-Armadillo (Armored Gyaos)
- 'Serpentine Gyaos' ('Long-Tailed Gyaos')
The alien invaders behind the Neo-Gyaos are cybernetic entities, often appearing as gigantic robots, or robotic vehicles, who share Gyaos genes in their biological half. It's never made fully clear, but it's possible that the Bio-Mechs may have attempted to invade Atlantis in the past and recovered some of Gyaos' cells, or are themselves Atlantean in origin. The Bio-Mechs are only now returning from deep space, to reconquer their birth-world. The written language and communication of the Bio-Mechs is the same as the Etrurian runes found on the atoll which Gamera was entombed.
- UFO (Bio-Mech Mothership)
- M-Machine-Dread VII
- Quicksilver (Dolphind)
- Nomad Viper
- 'Bio-Mech Air-Carrier'
- Nomad Chip
- 'Bio-Mech Fighters'
- 'Bio-Mech Hover-Blockade Drones' (separated units & combined)
- 'Bio-Mech Saucer Drones'
- 'Bio-Mech Sea Speeders'
- 'Bio-Mech Forest Walkers'
- 'Bio-Mech Beam-Barrier Drones'
- 'Bio-Mech Boomerang Drones'
In general, the game received positive reviews.