"LUCA" (Last Universal Common Ancestor) is based on Charles Darwin's proposition that all species of life have descended over time from common ancestors.

A high school student with amnesia tries to uncover what has happened to her. All leading her into deeper troubles ultimately revealing a darkness she could not have imagined.

Being bullied at school and suffering violence at home, Mi-rae, a middle school loner, lives on the border between reality and fantasy. The only places she feels restful are the computer game world, and the would in the novel she writes in her notebook. As her classmates Baek-hap and Tae-yang come close to Mi-rae, she gradually opens up her mind to them. In the meantime, the computer game service is terminated, and the world in her novel also disappears, leading Mi-rae to face a tough reality again.