The ME "memory extractor" is a technology developed through gate research, and was created by Mikhail Pavlichenko. The ME is used to extract, implant, and erase memories from people, it can even extract memories from recently deceased people. The ME was used on Suou, when she dies while she was younger. Her father (Mikhail Pavlichenko) extracted her memories from her dead body, and placed them into a doll. it was also used on both Mai, and Shinoda Chiaki, to erase their memories.
The ME was referred to a lot in the first season of Darker Than Black, yet it was never seen until the second season.