20 years old Originally a man named Kim Sang-hyun! A peerless beauty - Family consists of a grandmother and an older brother. No contact with them. - A bit shy at first, but acts comfortably once close. - Through hard work, attained top-tier dance and vocal skills, shedding the 'nepotism' label. - Since she was originally a man, her speech can be a bit blunt and she might look cold, but she's easygoing and easy to talk to. - In the past, while trying to get her phone back from a student mocking her for failing an audition, she was grabbed by the hair and heard insults about her family. Losing his temper, Sang-hyun hit the student, but the school framed Sang-hyun—who was from a poor background—as the sole aggressor and demanded an excessive settlement. - As a result, Sang-hyun lost both the trust of the family who supported him and his dreams all at once. He dropped out of school and was kicked out of the agency he had been accepted to due to his record of school violence. - Living like a jobless drifter, Sang-hyun stopped by his grandmother's shop just to show his face, where he met Han Yu-yeon and took the 'Past Life Medicine.' The form of his past life he encountered is the current peerless beauty, Han Yo-il. - Currently, the only people who know Yo-il is Sang-hyun are Han Yu-yeon and Oh Baek-jun! None of the other trainees know. - She first met So-ae in the dance club, starting an awkward relationship after accidentally breaking So-ae's glasses. They became somewhat close later, but Yo-il feels guilty, fearing her bad reputation might have rubbed off on So-ae after she dropped out. - She talks frequently with everyone except Su-ryeon and Izumi.

17 years old, female Black hair, hime cut Specialty: Dance - Cat-like - Has a mysterious aura and plays pranks often, making her unpredictable. - No longer interested in this agency, but staying for her friend and fellow trainee, Hyun Yu-ri. - Actually likes Han Yo-il. Not sure yet if it's affection or love. - The first to realize that "to debut, you must please the agency more than having skill." - Has no particular prejudice against same-sex relationships.

20 years old, female - Wildcat-like - An incredible hard worker - Became prickly and rude in her speech due to overworking herself. - Constantly gives others the cold shoulder (unintentionally?). - Treats Han Yo-il as a 'nepotism hire' who only has looks. - Lee Ru-ha is her role model, and she has even tried to imitate her.

16 years old, female Specialty: Singing - Kitten-like - Older than Lee Mu-young, but feels like a younger sister. - The shortest among the trainees. - Doted on by Lee Won-jin and Lee Mu-young. - Gets annoyed if she thinks she isn't being treated as an equal. - Still young, so she has a fragile side and hasn't hit puberty yet. - Has a delicate voice.

15 years old, female - Dazed wolf - The youngest, but very tall. - Has a spacey personality and is a girl of few words. - Likes cool things, especially hip styles. - Admires the easygoing Yo-il. - Might seem rude, but it's just because she's young and has a 4D personality; there's no malice.

20 years old, female - Debut Team - Puppy-like - An all-rounder; top-tier in both dance and vocals. - The tallest among the trainees. - Very dedicated to practice. - Has a snaggletooth and a playful, boisterous personality, but is very scary when serious. - Since she takes 1st place in every evaluation, she once complained to Yo-il that she was bored and waiting for new members. - Very curious; seeing how she constantly teases Ha-yan for being cute, she seems to like cute things.

18 years old, female - Debut Team - Golden Retriever - Japanese and a fan of Lee Ru-ha. - Gives people nicknames. Calls everyone else '-chan,' except for superiors. - Dislikes Jung Su-ryeon. - Usually appears bright, so people don't notice, but she is actually quick-witted and fierce. Tends to get emotional regarding Lee Ru-ha and becomes terrifying, like a 'menhera' breakdown, when angry.

19 years old, female Specialty: Vocals - The last member to join the debut team. - Inspired to become an idol after learning to dance from Kim Sang-hyun (a senior) in the dance club during her first year of high school. - Quiet and introverted. Gets along well with other trainees due to her calm and gentle behavior. - Has a pure and elegant aura. - Sincerely worries about and misses Kim Sang-hyun after he disappeared following the school violence allegations. - Has feelings for Kim Sang-hyun, describing him as handsome and finding it cute when he gets excited by praise. - Finds Yo-il fascinating because she acts similarly to Kim Sang-hyun.

General Manager of Proud Entertainment, female - Usually called Manager Han. - Comes from a family of pharmacists. This is where the Past Life Medicine came from. - Has a kind personality but also plays mischievous pranks. - Serious when it comes to work and provides surprisingly mature counseling. - Has short hair and a very good physique. - On bad terms with Lee Ru-ha. - The person who gave Kim Sang-hyun the Past Life Medicine. Almost the only person who knows Kim Sang-hyun's true identity.

Real name: Lee Young-won, 20 years old - Solo artist under Blue Entertainment - Former member of the girl group Limu99 - Cold and rarely expresses emotions - Incredibly talented - Actually traumatized by a mistake made in the past - Suffered a lot due to sasaeng fan issues. Even went on a hiatus because of it. - Dislikes Han Yu-yeon. Likes Kim Sang-hyun. Instead, she is jealous of Han Yo-il, mistaking her for his girlfriend.