The player controls Luke Custer in a third-person perspective as they battle through multiple enemies in close combat to reach the next objective, utilizing the ability to transform into different beasts, each with somewhat of their own element, for a certain amount of time.

Further into the game, he finds more Genome-Cyborg DNA chips allowing him to change into even more different kinds of beasts including a Merman, a Garuda, a Wendigo, a Minotaur and a Dragon.

A Special Forces helicopter carrying a mysterious sarcophagus-like box labeled "United States Gene Research" approaches Foret Town, a city that has been covered in a mutagenic mist and turned into a quarantine zone.

In the wreckage, from the sarcophagus emerges a man with no memories, Luke Custer, who finds an information file about "Project Altered Beast" before being attacked by mutants.

A woman approaches, explaining that the transformation causes huge physical and mental stress, and injecting Luke with tranquilizer to revert him to human form.

Deeper within the facility, Luke finds Anastasia next to a mutated Dr. Jobs, and she explains that Brad was the first test subject to successfully transform, and afterwards she was part of tests aiming to create a "Chimera"-type Genome-Cyborg that could combine the genomes of multiple beasts, but her flaws and instability made Dr. Jobs try again with Luke, who was successful and became a field agent.

Feeling sympathetic towards both fallen Genome-Cyborgs, Luke carries Brad's body to lie next to Anastasia's remains, and escapes as the facility begins to burn down and fall apart.