Tatsuya was born as the second son of three brothers. His mother, Yumi, had the impression that he was a quiet child who did not assert himself. One spring, his older brother got a job and lived alone, and his younger brother enrolled in a boarding school on the recommendation of sports. Her father moved away from home and her life changed rapidly, and the mother and son started living together. Yumi feels a sense of loss when her lively house suddenly becomes quiet. Seeing her mother's condition, Tatsu