Nan-young is initially disqualified from the Mars expedition because psychologists perceive her stoic facade as a symptom of unaddressed trauma. Her time with Jay softens her defense mechanisms, allowing her to process her mother's death. When a reserve spot opens up on the crew, Jay—despite his personal heartache—encourages her to accept it and pursue her calling.
During the mission on Mars, Nan-young locates the original, collapsed habitat where her mother perished. Using her prototype Life Form Detector and the seeds passed down to her, she successfully sprouts plant life inside the Martian soil. At the same time, she receives Jay's completed musical composition, which he finished in Seoul using analog instruments.
The ending does not offer a simplistic romantic reunion on Earth. Instead, it shows both characters thriving in their individual callings—Nan-young discovering new horizons on Mars and Jay re-establishing himself as a fulfilled composer in Seoul—bound eternally by mutual love and emotional support across the universe.