Eriko was one of Miyoko Tanashi's roommates at the Orphanage and was the closest thing she had to a friend there. It's not known how she came to the institute, though it can be assumed that she lost her parents like the others due to the war or some other incident. At some point, she arranged with Miyoko and two others to escape from the orphanage and get to a much better one called the House of Love. They tried to escape and despite Miyoko getting the furthest, all of them were caught and punished for their attempt. Eriko was sent to the chicken coop where she was violently pecked to death by the chickens and had her eyes gouged out, much to Miyoko's horror. Eriko's fate is not revealed in the anime.

(Source: wikia)