Echo Girl (real name Choi Kyungju) is a side character who is involved in 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. She 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.
She is a pretty girl with a pale complexion, wide bright blue eyes, and medium-length caramel hair that curls slightly at the ends. She has stated that she has natural D cup breasts. She is seen wearing a short navy blue dress, and it is mentioned that she wears heels.
Echo Girl comes from a wealthy family whose father can be considered has a big influence. She has been a fan of Zen for a long time and been sharing how she feels about Zen in her social media even before she made a debut as a singer.
Echo Girl seems very eager to act with Zen, so eager that she gave him a leading role just so they could act together. She is a big fan of Zen. She has gone to Zen's house once she heard news of his injured ankle and has shown 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 a RFA party but had been ignored.
When confronting him about getting her revenge on the guys in the RFA, she is ignored yet again. This results in her telling Celebrity A! News that Jumin Han, the Chairman in line of C&R International, is a homosexual.
- She has seen "Jalapeños Topping was Pretty Spicy" more than ten times and knows all the lines by heart.
- She seems to hate being called by her real name.
- It is hinted that she is in Zen's fan club.
- She once modeled for a branch company in C&R International for their heart-shaped vitamin pills. This is how she knows Jumin Han and has his number.
- She feels like she's just working when people call her "Echo Girl".
- She refuses to eat food that she believes will make her fat.
- Yoosung has stated she's so famous her photo books sell out within minutes and any songs she release are number one on the charts.