Echo Girl (real name Kyungju Choi) is a side character who is involved in the majority of Zen's route, and can be considered as the antagonist in the events of his route.
She is a young flirty idol and a fan of Zen that is always trying to hit on him, as shown in many of Zen's visual novel mode events.
Echo Girl has an overindulged personality who tends to believe that she can get everything she wants and trusts her father to back her up. As seen from the Zen scandal she started, she is desperate for attention.
Echo Girl is a pretty, pale-skinned girl. She has medium-length, wavy brown hair and side swept bangs, wide bright blue eyes and, in her own words, beautiful, natural D-cup breasts. She is usually seen wearing a knee-length, navy blue dress and it's mentioned that she wears heels.
Echo Girl comes from a wealthy family and her father can be considered a big influence. She's been a fan of Zen for a long time and shared how she felt about him on her social media even before she made her debut as a singer.
Echo Girl is a big fan of Zen and seems very eager to act alongside Zen, so eager in fact, that she gave him a leading role just so they could act together. She also went to Zen's house once she heard the news of his injured ankle and showed great concern.
After being rejected by him, she claimed to Celebrity A! News that Zen called her to his house and sexually harassed her.
Echo Girl has previously modeled for C&R's branch company for their heart-shaped vitamin pills. She has also texted Jumin Han to ask to be invited to the RFA party but was ignored.
When confronting him about getting her revenge on the guys in the RFA, she was ignored yet again. This resulted in her telling Celebrity A! News that Jumin Han, the Chairman in line of C&R International, was homosexual.
- Echo Girl has seen "Jalapeños Topping was Pretty Spicy" more than ten times and knows all the lines by heart.
- Echo Girl seems to hate being called by her real name (Kyungju Choi).
- It is hinted that Echo Girl is in Zen's fan club.
- Echo Girl once modeled for a branch company in C&R International for their heart-shaped vitamin pills. This is how she knows Jumin Han and she has his number.
- Echo Girl feels like she's just working when people call her "Echo Girl".
- Echo Girl refuses to eat food as she believes will make her fat.
- Yoosung has stated she's so famous her photo books sell out within minutes and any songs she releases are number one on the charts.
- Echo Girl has a song named "Free Friday".