Season 1

On the first day of school, high school freshman Joo-young falls deeply in love at first sight with the pretty but aloof Ja-rim and thinks they are destined for one another.

Joo-young surprises Ja-rim with loads of lollipops on White Day. Ja-rim gets annoyed as Joo-young keeps on following her and asking for her number.

Joo-young, Kyung-woo and Byung-hoon prepare for a dance number at the school retreat talent show. When students arrive at the retreat's venue, Joo-young suddenly goes missing.

Joo-young publicly confesses to Ja-rim at the talent show.

Joo-young overhears Ja-rim telling her friends she went along with Joo-young's public confession because she pitied him. Hurt by her words, Joo-young keeps on whining to his friends not to pity him.

Joo-young decides to formally confess to Ja-rim and ask her to be his girlfriend on Rose Day. A female senior tries to stop Joo-young from going out with Ja-rim.

Joo-young is in ecstasy when Ja-rim finally accepts him as her boyfriend, but she remains as cold as before. Ja-rim flat out rejects Joo-young's date plans and reminds him of their upcoming exams.

Joo-young manages to get angry at Ja-rim and complains for being treated so badly.

Kyung-woo's friends discover that he is working in a café and is popular among female customers. They pay him a visit one day, unknowing that it is Byung-hoon's birthday. Byung-hoon innocently assumes they are preparing a surprise for him.

Joo-young, Ja-rim and their friends go on a trip to Byung-hoon's countryside home. When they get thirsty while harvesting chilies, Joo-young goes to fetch water but returns drunk after not being able to stop himself from drinking alcohol.

Before going home, Joo-young, Ja-rim and their friends clean Byung-hoon's grandparents' house and have fun for the last time. Ja-rim tries to make hangover soup for Joo-young.

Joo-young goes out for a date with Ja-rim, who is unknowing that it is Joo-young's birthday.

Joo-young asks Ja-rim to cheer for him in a recreational basketball match with Jung-woo. Ja-rim meets Jung-woo and runs away in surprise. A misunderstanding ensues and Ja-rim finds it hard to explain to Joo-young the truth of her past with Jung-woo.

Joo-young receives a call from Min-ji. The day after, Joo-young goes to play basketball with Jung-woo in casual attire and behaving strangely.

Joo-young has an upcoming weekend date with Ja-rim but he discovers that his allowance is running out.

In the school festival, Class 1-3 becomes a customer magnet with their café and picture taking with the most famous students of their class, Kyung-woo and Ja-rim. Byung-hoon, Joo-young and their classmates carries out a hilarious plan to steal Class 1-3's customers and save Class 1-2's face.

After an encounter with middle school acquaintances, Kyung-woo suddenly goes missing for two days. He returns to school but has become hostile to Joo-young. To find out what could have happened to him, Joo-young and the remaining friends talk about Kyung-woo and Joo-young's middle school past.

Kyung-woo realizes he mistakenly thought Joo-young betrayed him by spilling the truth of his long bangs. He reflects on their friendship and apologizes to him.

Ja-rim accidentally sees Joo-young naked. Joo-young becomes embarrassed and stays away from Ja-rim. Kyung-woo starts having feelings for Ja-rim but he goes to hang out with Ye-seul instead.

Class 1-3 remains in last place during exams because of Kyung-woo's low scores owing to his laziness in studying. Kyung-woo's friends and the entire Class 1-3 force him to study in order to save the class' face.

Joo-young, the shortest among their circle of friends, notices Ja-rim's growth spurt and worries she might overtake him. He scrambles to gain height by doing all sorts of exercises and eating height-related foods.

The students of Isam Information High School become hooked to playing milk caps (ttakji) using chicken coupons. Ah-ram gets the hang of it and begins to take the lead. Tasting glory, she challenges Kyung-woo, who has defeated many of his peers, to a match.

Joo-young ponders about having little "skinship" with Ja-rim compared to other couples. Kyung-woo's relationship with Ye-seul is put to the test when they go to a double date with Joo-young and Ja-rim at Lotte World.

The cafeteria is under emergency repairs, so Ja-rim decides to pack lunch for her and Joo-young despite being a lamentable cook. Min-ji goes out with her admirer Sang-hoon, but she learns later on that her crush Kyung-woo has broken up with Ye-seul.

Fearing his mother's wrath, Byung-hoon decides to skip playing games and study for the exams, but his attention is diverted when she meets and gets attracted to a pretty college girl at the library. Ji-soo confesses his feelings to Ah-ram.

Joo-young's grades dropped, prompting his mother to tell him to move out from his apartment and live with his parents once again. His friends decide to hold a send off party for Joo-young.

All Grade 11 students are mandated to retake an exam and Classes 1-2 and 1-3, the last to take the exam, have to stay until nightfall. After the exam, Jin-hee suggests playing an item retrieval game among the friends to test their courage, much to scaredy-cat Kyung-woo's worry.

Joo-young starts receiving text messages from his ex-girlfriend Bo-kyung, unknowing of her ulterior motives. As he gets worried that Ja-rim will know about it and misunderstand him, Joo-young runs into Bo-kyung while he is with Ja-rim. Soon, he notices that Ja-rim is not getting angry with him and has started to treat him nicely.

Kyung-woo reveals to Ja-rim the truth about Bo-kyung. Ja-rim decides to deal with the situation herself and confronts Bo-kyung, much to Joo-young's shock.

Joo-young prepares a secret special event for Ja-rim but things seemingly do not go as he planned.