"Eve Zero" is a prequel to the famous detective/mystery adventure Eve Burst Error. You control once again the two main heroes of the series: the witty and womanizing private investigator Kojirou Amagi, and the beautiful red-haired secret agent Marina Houjou. The events of the game take place shortly before those of "Eve Burst Error". Kojirou is working at Katsuragi Detective Office together with his girlfriend Yayoi. Dr. Nishina, the head of a genetic research facility, hires Kojirou to investigate the disappearance of his son Shin. At the same time, Marina receives an assignment from her boss Kouno, which involves watching over a representative of an American company. As in all EVE games, the two stories appear unrelated in the beginning and are gradually linked together later in the game.
You need to switch between the two protagonists in order to advance in the game. The interface consists of a menu that makes it possible to interact with the game world. Beside the traditional "Look", "Talk", and "Go" commands, there are many others, specific to the situation. This is a Japanese-style adventure game - an interactive story without puzzles.