The episode begins with a flashback to Hori Kyosuke's school days, where he meets Sengoku Takeru and Koyanagi Yuriko. Kyosuke is a first-year student, and Sengoku is the student council president in his third year. Kyosuke helps Koyanagi carry boxes for the student council, leading to an interaction between the two. Koyanagi is a third-year student with a straightforward and easygoing personality. Kyosuke develops feelings for her, but she graduates before anything significant happens between them.

In the present, the episode focuses on the daily life of the Hori family. The now-adult Kyosuke still lives with his family. His younger sister Kyoko attends high school, and his younger brother Sota is in elementary school. The family has a lively and sometimes chaotic atmosphere, and Kyoko often gets annoyed with Sota for leaving his things around the house. Kyosuke tries to mediate between the two, but his efforts often backfire.

Kyoko is hot-tempered and easily irritated, especially when it comes to her family. She argues with Sota about household chores, leading to a heated fight. Kyosuke tries to calm her down, but she storms off angrily. Later, Kyoko and Sota make up, and Kyosuke reflects on his role as the older brother.

Toward the end of the episode, Kyoko writes an essay about her family, which is praised by her teacher. The family gathers to read the essay, and it turns out the essay is titled "My Big Brother" and focuses on Kyosuke.