Ko Eun (고은), better known as Koeun (고은), is a trainee in SM Entertainment, and a member of the pre-debut training team SMROOKIES, established in 2013. She was introduced on July 8, 2015.
- She was born on March 18, 1999 in Seoul, South Korea.
- Koeun said in a Ceci 2015 interview that she was a Track and Field athlete in elementary school.
- She was a registered 80m track and field athlete in the Korea Association of Athletic Federations, who represented Gyeonggi Bongilcheon Elementary School in Paju, Gyeonggi Province.
- She stopped competing now and is no longer registered, so her KAAF profile says she is a "retired player."
- Her specialty is Vocals.
- Her nickname is Koleader.
- Her hobby is doing yoga.
- She was in the lineup to debut as a Red Velvet member.
- Yeri and Koeun are good friends.
- Koeun joined SM Entertainment in 2011, training for 7 years as of 2018.
- In April 2017, she was featured in Yesung's "Paper Umbrella" music video, along with fellow Rookie Jungwoo.
- Later in 2017, Koeun with fellow SM Rookies Hina and Ningning sang several OST for the MBC animated series titled Shining Star.
- They sang the opening theme, "Shining Star", and original songs titled "Dream Dream Dream", "Someday" and "Run and Run."
- They also covered Girls' Generation's "Into The New World", "Gee", f(x)'s "Ice Cream", BoA's "Moto", and SES' "I'm Your Girl."
- It was confirmed that one of the songs of Shining Star, Girls' Generation-TTS' "Checkmate" was covered and sung alone by Koeun.
- Koeun also sang with Onestar for a duet version of "Someday."
- MOTTO: "Think positively, act aggressively."
- "The cute maknae Koeun is now Ko-leader."
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