Released in 1998 as a sequel to the 1995 novel by 瀬名秀明 (Dr. Sena Hideaki, a Japanese novelist), Parasite Eve (パラサイト・イヴ) was Squaresoft (now Square Enix)'s answer to Capcom's Resident Evil/Biohazard series' booming success. The original novel also spawned a film adaptation in 1997, and Square released a sequel to the game (Parasite Eve II) in 1999. Like RE/Biohazard games, Parasite Eve combines elements from the RPG, shooter, and survival horror genres. The main weapons in the game are guns of various sorts, but you also get Parasite Energy, a variation on a typical RPG's concept of magic.

The year is 1997; the time, Christmas Eve. NYPD police officer Aya Brea finds herself on a date to the opera with some rich snob who's been pestering her for a night on the town. Fortunately she doesn't have to put up with him for long, since as soon as they sit down everyone else in the audience bursts into flames. Aya's night quickly turns even weirder, with the lead actress oscillating between lecturing Aya on mitochondria, attacking Aya with strange powers, and transforming herself into some bizarre creature. Melissa, or "Eve" as she now calls herself, is not the only thing being transformed in the city. Most humans spontaneously combust in her presence, but other animals mutate into vicious creatures with powers similar to Eve's.

What is going on in New York? Who is this Melissa/Eve girl, really? And what exactly do mitochondria have to do with anything? Jump into the shoes of Aya Brea and try to find out the answers to these questions before all of New York, and perhaps even the world, succumbs to Eve's chaos!