Season 1

While filming a movie in a high school, idol-actor Yoon Sul-chan from the fictional group Man in Black becomes involved in a scandal. Jeopardizing MIB’s new album release, his label company decides to send him to school for 3 months.

As the second new transfer student at the school, Sul-chan has no choice but to sit next to Min Se-yi, who has developed a strong dislike towards him from an event that occurred in the first episode. All For One bluntly rejects Teacher Dok-go's request to play at a charity event, and we're introduced to "Adam", a mysterious man in the park who seems to know the song Se-yi sang out loud.

Excluded from his assigned music group to earn his solo grade, Sul-chan plays the song he heard Se-yi perform in the park, replacing it with his own comical lyrics. After an event at the shrines, the students are called to the office and forced to come up with something to perform at the charity event or risk having their reputation tarnished.

We have already seen that there is a history between Sul-chan and Se-yi, Sul-chan and Jung Sun-woo, Adam and Se-yi, and (last but not least) "Radio" and Cha Do-nam. Now, in this episode, we have also confirmed that there is definitely something between Sul-chan and his mother that has yet to be revealed.

All For One decides to participate in the charity event. This leads Sul-chan’s group to be removed from having to perform. Ma Joon-hee, the All For One leader, convinces the teachers to allow All For One and Color Bars to battle against each other to decide who will perform in the charity event. Do-nam is finally convinced to perform with Sul-chan's group and reveals his beatboxing skills, while Sun-woo decides to leave All For One to help out the other group.

Se-yi finds out that Sun-woo is her childhood friend, and Kim Na-na's feelings are revealed. Se-yi overhears a portion of the conversation Sul-chan is having with Sun-woo, admitting his feelings for her, but misunderstands the subject of his attraction.

Na-na's powerful singing voice excites the group, making her the new lead singer, and finally, the battle between All For One and the Color Bars takes place.

Color Bars lose to All For One, so Sul-chan uses his disappointment as an excuse to ask Se-yi out on a date, but they are put in an awkward situation by a reporter. Se-yi is upset when her mother suddenly comes back from New Zealand, and Sun-woo confesses his feelings. Radio and Do-nam's past is revealed.

Radio is embarrassed when he is rescued from an attempted suicide and seeks out Adam. Sul-chan has to go to Japan to film a music video, but this provides an opportunity for Se-yi to decipher her feelings.

Embarrassed by the spontaneous kiss, Sul-chan and Se-yi part, confused. The next day, Se-yi spends the day thinking about Sul-chan, who appears at school late. Na-na opens up to Sun-woo and asks him to teach her how to play the bass. When Eun-ha realizes Sul-chan and Se-yi's attraction to each other, she is heartbroken.

Sun-woo can't help but feel saddened that his first love is interested in someone else. A producer from JDC scouts the school for a band battle and sets up a rematch between Color Bars and All For One, but Sul-chan has his group's comeback to worry about. Adam's past is revealed, and Sul-chan confides in Se-yi about how his friendship with Sun-woo became tarnished. Se-yi makes her decision between Sul-chan and Sun-woo.

Despite being rejected, Sun-woo is fired up to compete against Sul-chan for Se-yi, and once again, Color Bars go against All For One for the variety show 'Kiss of the Goddess'.