An elementary school student named Tsubaki carries a deep sense of responsibility for a scar he accidentally left on the eyebrow of his childhood friend, Yuu, when they were playing together years ago. Driven by this guilt and a growing, heartfelt devotion, Tsubaki makes a firm decision to grow up big and strong so he can become someone capable of protecting Yuu and making him happy. The central complication of his mission is the significant gap in their ages and stages of life; Tsubaki is still a child in elementary school, while Yuu is already a kind and gentle, but rather naive, high school student.

The story focuses on Tsubaki's determined, often comedic efforts to be seen as more than just a kid by the older boy he admires. Yuu, for his part, is largely oblivious to the romantic nature of Tsubaki's feelings, treating him with tender affection but continuing to see him as the young child he has always watched over. This dynamic creates a sweet and awkward push-and-pull, where Tsubaki's earnest advances are frequently deflected by Yuu's innocent and apathetic personality. Supporting Tsubaki in his quest are his classmates, particularly a friend named Higa, who is more knowledgeable about romance and encourages Tsubaki to pursue his feelings, often offering strategic, if childish, advice.

The narrative is a slice-of-life and romantic comedy that explores themes of first love, the confusion of growing up, and the blurry line between childhood affection and adolescent yearning. The story maintains a light and cute tone, emphasizing the characters' emotional growth and the evolution of their bond as they navigate their daily lives together. Originally a web manga by Miyuki Nakayama that began serialization in 2020, the series has gained a following, leading to the announcement of a television anime adaptation expected to air in the near future.