How I, an only child, ended up as one of four sisters

The protagonist, Morishima Yuuki, a disillusioned office worker in a black company, collapses from heat exhaustion on a sweltering Obon holiday. He awakens to find himself reborn as a baby girl, one of quadruplets, in a wealthy family named Nishiyotsutsuji. This new life is a stark contrast to his previous one; he is now a member of one of Japan's three major financial groups. He learns his new name is Yudachi, and his sisters are Asahi, Mahiru, and Yoru.

Over the next three years, Yudachi, retaining his adult consciousness, develops rapidly. While his sisters can speak simple phrases, Yudachi is fluent, surprising his parents, Reika and Takeru. He finds the mundane activities of childhood, like playing house, tedious, but participates to avoid upsetting his mother and sisters. He also learns he has an older brother, Kanato, who frequently joins their games. Yudachi resolves to acquire enough academic skill to secure a white-collar job independently, ensuring he doesn't repeat his past mistakes.

At age five, the quadruplets begin attending kindergarten. Yudachi, being the most articulate, often takes the lead in interactions. His sisters are initially shy around other children, but soon adapt. Yudachi, however, finds it difficult to fully embrace childhood play, though he participates. He is often roped into being "it" during games of tag, a role he initially resists but eventually enjoys.

Two years later, at age seven, the quadruplets prepare for entrance exams for the prestigious Shirayuki Gakuin Elementary School. Their father, Takeru, coaches them extensively in interview practice. Yudachi excels, having a significant advantage due to his past life's experiences. His sisters struggle initially but improve with practice. The entrance exam day arrives, filled with anxiety for the sisters, but ultimately, all four are accepted.

Following their acceptance, the sisters indulge in unrestrained play before their kindergarten graduation. As graduation approaches, the impending separation into different classes at Shirayuki Gakuin causes sadness among their classmates. Yudachi reassures them that they can still play together, easing their worries. During their final kindergarten playtime, Yudachi is once again tricked into being "it" during a game of tag, a humorous callback to their first day.

The narrative then shifts to the Shirayuki Gakuin entrance ceremony. Yudachi, now dressed in a girls' uniform, feels a sense of dread about the challenges of making friends. The school is incredibly vast and well-equipped. After the ceremony, the students are led to their classrooms. Yudachi and Mahiru are placed in the same class, while Asahi and Yoru are separated. Yudachi reassures his sisters that they will still see each other during breaks. He also has to manage Mahiru's tendency to look at him during class. The first day concludes with the students introducing themselves, and Yudachi's and Mahiru's similar appearances cause a stir. The day ends with the assignment of extracurricular activities: piano, swimming, ikebana, and foreign language.