At just 12 years old, Azusa Noyama, known as Azuki-Chan despite her distaste for the nickname, is a fifth-grade student. When a new classmate, Yuunosuke Ogasawara, takes an interest in her nickname, expressing his fondness for it, Azuki finds herself developing feelings for him. Their bond deepens as they share a diary, ultimately blossoming into a young romance as they become a couple.