The narrative follows the protagonist, formerly Matsudayoshifumi, a 39-year-old man who suffered from a debilitating illness and despair in his past life. He is reborn as a four-year-old girl named Matsuda Sumire, retaining his memories. Sumire is determined to live a fulfilling life in this new existence, reflecting on his past regrets. She struggles with a complex about her past family relationships and her appearance, feeling that her current cuteness is diminished by her adult consciousness.
Sumire's family consists of her older sister, Matsuda Tsukiko, who harbors intense jealousy towards Sumire's charm and popularity; her father, a workaholic who instilled fear in his son; and her mother, who is frail and believes her own perceptions are absolute truth, having contributed to Sumire's past illness. Sumire also reconnects with her childhood friends, Okamoto Nao and Takahashi Fumika, whom she deeply cares for, especially Nao, whom she wants to protect from a potentially tragic future.
The story progresses through Sumire's early childhood. She attends kindergarten, where she befriends Nao and Fumika. Sumire, despite her adult mind, navigates childhood social dynamics, often finding herself in a leadership role due to her helpful nature. She also experiences the subtle but persistent animosity from her sister Tsukiko, who resents Sumire's favored status with their grandparents and the attention she receives. Sumire, with her adult perspective, tries to foster a better relationship with Tsukiko, understanding her sister's jealousy as a childish reaction.
As Sumire enters elementary school, she is placed in the same class as Nao and Fumika. She encounters her former childhood friend, Masataka (Ma-kun), who lives next door and is now a senior student who looks out for her. Sumire also begins to develop a more mature understanding of her family, recognizing her mother's struggles and her father's distant nature. She starts attending the town library's study room, where she befriends Kiyohara Chika, a high school student. Sumire uses this time to proactively study, aiming to get ahead and ensure a more stable future.
A significant turning point occurs when Sumire and her friends, Nao and Fumika, are invited by two boisterous classmates, Tanaka Yuji and Yasui Ippei, to explore an abandoned truck garage. Despite Sumire's apprehension due to the dangerous conditions and Fumika's fear, they are goaded into joining. This adventure highlights Sumire's protective instincts and her growing bond with her friends, particularly Fumika, who shares her reluctance. The chapter arc concludes with the formation of this reluctant exploration group, hinting at potential dangers and further character development.
Throughout these chapters, world-building elements include the societal norms of the era, particularly regarding children's behavior and education. Sumire's internal monologue reveals her past life's struggles with illness, societal support systems, and her profound desire for a different life, which she is now experiencing as a young girl. The narrative emphasizes Sumire's goal of living a fulfilling life, cherishing her relationships, and learning from her past mistakes.
