The Yuzuki brothers, consisting of the eldest son, Hayato; the second son, Mikoto; the third son, Minato; and the youngest, Gakuto, have been living together since they lost their parents two years ago.

Minato first met his best friend Uta when they were elementary school students. Uta, who moved next to the Yuzuki family, responded coldly to Minato and Mikoto. Determined to become friends with Uta no matter what, Minato enthusiastically keeps inviting them to play, but...

A class observation day was scheduled to be held in Gaku's class. However, Gaku was worried that if Hayato took a day off to attend, it would cause inconvenience at his workplace and increase his workload.

Gakuto is keeping his class observation day from Hayato by using a stand-in.

The Yuzuki family's four brothers cherish each other deeply. Among them, the second son, Mikoto, dotes on Minato, the third son, while Minato, in turn, adores Gakuto, the youngest.

Hayato catches a cold. Mikoto, Minato, and Gakuto are eager to care for Hayato and handle the household chores. Even when they run into the Kirishima family on their way to a trip, they keep Hayato's condition a secret, not wanting to worry them before their vacation.

Gakuto won a diary. Wondering what to write as the entry, Mikoto mentions, "You can also write about your thoughts and feelings." Encouraged by this, Gakuto chronicles the daily happenings in the Yuzuki household...