Throughout the film, indirect visual hints are shown that describe the events preceding the main story. Most details are seen through Sammy's reverse chronological flashbacks and the final chronological credit montage, although some information comes from brief displays of code seen throughout the film. What follows is an unconfirmed summary of the backstory formed by piecing together these visual clues with the rest of the plot.
Shiotsuki created the initial android AI, code:life. Over time, tensions between robots and humans increased. Human anti-robot organizations were formed, including the Ethics Committee. Shiotsuki's bionic arms suggest that he was injured at some point by one of these groups. At some point, the Ethics Committee attacked Nagi and her robot in the mysterious Tokisaka Incident, causing her severe injury which includes the loss of her arms. Upon seeing what pain his robots (indirectly) caused her, Shiotsuki built her bionic limbs, seen in the final scene as subtle mechanical joints in her hand. Through the process of her rehabilitation, the two grew close. After Nagi fully recovered, she and Shiotsuki decided to do something about human and android relations, seeing how deeply this issue has affected each of them.
Shiotsuki created a café sign which broadcasts the 1138 override protocol. This protocol has higher priority than the suppressive portions of the code:life AI and allows androids to act more freely, including removal of their halos. It also attracts androids to the café sign ("Are you enjoying the Time of Eve?").The protocol is spread from robot to robot. Shiotsuki and Nagi set up different cafés in the countryside as safe spaces to allow robots and humans to come together and socialize. However, the cafés were shut down and their patrons destroyed by anti-robot mobs, forcing them to try again at a different location.
In response to these failures, Shiotsuki created the code:eve AI in an attempt to allow androids to better express their suppressed emotions and feelings. He argued with Ashimori, and future head of the pro-robot Android Promotion Committee (APC). She wouldn't allow the line between machine and human to be blurred any further, causing Shiotsuki to leave the APC. His parting gift was the first prototype code:eve android, Sammy. Dr. Ashimori is forced to destroy Sammy, but regrets it. The APC repairs Sammy and Dr. Ashimori secretly allows her to live in an APC member's (Rikuo's father) house. Nagi and Shiotsuki moved to the city and set up the current "Time of Eve" café. Current APC activity is observational. Setoro, the man in the suit at the café, reports back to Dr. Ashimori.
The type of CPU used by the Calvin-4 is an "R.U.R." R.U.R. refers to the 1921 play by by Karel Capek (subtitled "Rossum's Universal Robots"). The play introduced the word "robot," from the Czech word "robota", meaning "forced labor".
The "Calvin-4" robot was chosen by the "Ethics Committee" to conduct the preliminary investigations of places that encourage "inappropriate" human-robot interactions. "Calvin-4" is an allusion to Dr. Susan Calvin, a fictional character in some of Isaac Asimov's robot stories. Susan Calvin was the chief "robopsychologist" at US Robots and Mechanical Men, Inc., the major manufacturer of robots in Asimov's 21st century. She appeared briefly as a college student toward the end of Asimov's short story, "Robbie," and was the main character in about one-third of the short stories in Asimov's The Complete Robot (1982).