The OVA episode, referred to as episode 10.5, depicts events occurring somewhere within the timespan of episode eleven of the series. The series is based around the efforts of humanity to quarantine and eradicate the diclonius, a species of mutant humans with horns. It focuses on "Lucy", who escapes her holding facility and is believed to be the first diclonius, and on two teenagers, Kohta and Yuka, whom Lucy encounters in the Japanese city of Kamakura.
The OVA episode 10.5 takes place within the timeframe of episode eleven of the series. The story revolves around humanity's efforts to contain and eradicate the diclonius, a species of mutant humans with horns. It centers on "Lucy", who escapes from captivity and is believed to be the first diclonius, and two teenagers, Kohta and Yuka, whom Lucy encounters in Kamakura, Japan.