Eiko Shimamiya (島みやえい子, Shimamiya Eiko?, born April 20 in Sapporo, Japan), also called EIKO or PEKO, is a female J-pop singer and a former member of the production group I've Sound. She is best known for singing the opening themes of the anime series Higurashi no Naku Koro ni. Eiko also handles a school called Shimamiya Size (S-size) in Sapporo. Some of her former students include I've Sound singers Mami Kawada, Kotoko and Kaori Utatsuki. She announced on May 10, 2010 via Twitter that she was diagnosed with thyroid cancer. Her "Perfect World Live Tour", which was scheduled to begin in June, was subsequently canceled. She made an announcement of her full recovery from cancer on January 28, 2011.