Chizuru, a 35-year-old single mother, works tirelessly day and night to raise her son. She carries a deep loneliness watching other couples at school events, yet finds strength in her child's smile. When her son enters fifth grade, his new teacher is Takeuchi—a taciturn, expressionless man. Initially, Chizuru sees him as unapproachable. But when her son faces troubles at school, Takeuchi visits repeatedly, earnestly explaining her son's behavior. For the first time, Chizuru recognizes a reliable