Jung_E portrays a desolated Earth in the 22nd century that is no longer habitable due to climate change, and humans are forced to live in man-made shelters built in space. As the humans settle in around 80 of those shelters, three of them declare themselves as the Adrian Republic, attack Earth and other shelters, and cause a civil war between the Allied Force and Adrian Republic.

Captain Yun Jung-yi is a legendary mercenary of Allied Forces who led her team to countless successful missions against the Adrian Republic. She has a little daughter, Yun Seo-hyun, who suffers from a lung tumor, and Jung-yi became a mercenary to afford her daughter’s medical treatments. The day Seo-hyun gets the surgery, Jung-yi fails her mission and ends up in a coma. Kronoid, an institute in charge of developing AI technologies, convinces her family to agree to clone her brain, promising that they will cover Jung-yi’s treatments, her daughter’s education and living expenses.

Thirty-five years later in 2194, Kronoid clones Jung-yi’s brain to develop an AI mercenary, code-named Jung_E. Dr. Yun Seo-hyun is the team leader of research project Jung_E and seeks to memorialize Jung-yi as a hero rather than a failure. Researchers at Kronoid have copied Jung-yi’s brain data and put them in android bodies. Through simulations of Jung-yi’s final mission, they try to extract combat memory data that could be used to develop an exceptional combat AI. Just like Captain Jung-yi failed her last mission, AI JUNG_E also fails in every simulation of the last mission.

Seo-hyun learns that her childhood cancer has returned, and she only has three months left to live. She also learns through the chairman of Kronoid that there is no need to develop combat AI anymore because the Adrian Republic and Allied Forces are entering a treaty. With peace approaching, the company has decided to focus on household services. Seo-hyun discovers one of her team members with a scantily clad Jung_E robot in his apartment, but he claims that Kronoid has tasked him with investigating using the Jung_E models as sex toys. After the last simulation of project Jung_E, Seo-hyun escapes the facility with a Jung_E robot while other combat robots and security forces chase them. Kim Sang-Hoon, the project’s director, is revealed to also be a robot with an AI brain. Kim shoots Seo-hyun as she and the Jung_E robot flee via elevated rail. The Jung_E robot fights him off, and he is destroyed when his part of the train falls to the ground. Seo-hyun urges Jung_E to leave her and survive. After surprising Seo-hyun by showing affection, Jung_E escapes and looks around on top of a rock in a mountain range.