Okuno Kokoro, a high school freshman, sits down for her first class and notices all the students have different sleeve lengths. When she secretly follows her classmate after school, she finds herself at a "sleeve salon."
Kokoro's classmates started speaking in various dialects, thanks to a popular new lipstick. After finding a lipstick stand, she buys a lipstick from a certain region and goes to someone's house.
Kokoro's growling stomach catches the attention of the captain of the Belly Bell Club, a club focused on creating harmonies with people's growling stomachs. Kokoro and her childhood friend decide to participate in the club concert.
Kokoro's social studies teacher takes her class to a farm that specializes in making navy blue socks from hollowed-out eggplants. When she and her classmates return to harvest the finished socks, Kokoro's are missing.
Kokoro's classmates try to lose weight by eating tiny lunches. Asuka and Suzu reveal that they make up for it by making "air donuts" after school that won't make them gain weight. However, there seems to be a hidden catch.
Kokoro and Kotaro's math teacher off-handedly mentions an urban legend about "miracle mathematics," when a student "suddenly became good at math." Kokoro ends up in the nurse's office, where she learns about the secret of "math muscles."
Kokoro is bored after school, when all her other classmates are busy with club activities and salon appointments. She discovers Killing Time Park, where the caretaker tells her she can kill time to use later, on an important occasion.
Kotaro falls asleep while hiding in an empty classroom and wakes up in the middle of a "girls' language" lesson. He can't keep up, but when he suddenly remembers.a letter written by a female classmate, a big commotion ensues.
While cleaning after the graduation ceremony, Kokoro discovers many "seishun-dama" stuck to the gym ceiling, or balls that represent the regrets of graduating students. A monk offers a memorial service for the balls, but one ball remains.
