In this dark, previously untold chapter of Steins;Gate, we follow the quirky mad scientist Okabe as he grapples with the aftermath of his unsuccessful attempt to save Kurisu. Disheartened, he decides to abandon his vibrant scientist persona in an effort to leave the past behind. Just as life seems to return to normal, he encounters someone connected to Kurisu who reveals that they are experimenting with a device capable of storing human memories and creating a simulation of the person, complete with their traits and personality. As Okabe begins to test this device, he discovers that the simulation of Kurisu not only revives his old sorrows but also introduces new, unforeseen tragedies.

Zero serves as a companion story that delves into the future events of the Beta Attractor Field, which play a crucial role in making the conclusion of the original narrative possible.