Satoko, portrayed by Hiromi Nagasaku, and Kiyokazu, played by Arata, are a couple navigating the challenges of parenthood as they raise their adopted son, Asato, who is voiced by Reo Sato. Their journey begins with turmoil when they receive an alarming phone call from Asato's kindergarten teacher. A fellow student claims that Asato pushed him off the jungle gym, a statement that Asato vehemently denies. The incident escalates when the boy’s mother demands compensation for her child's medical expenses, leading Satoko to question whether their son might have inherited adverse traits from his birth parents.
In a poignant flashback, we learn about Satoko's and Kiyokazu's early struggles to start a family, including Kiyokazu's diagnosis of aspermia. After a heart-wrenching and unsuccessful series of medical treatments, the couple resigns themselves to a childless existence. However, inspiration strikes as they catch a program about Baby Baton, a nonprofit organization dedicated to pairing infertile couples with mothers who are unable to care for their biological children. Realizing this could be their path to a fulfilling family life, they choose to adopt.
When they finally bring newborn Asato home, they are given the option to meet his biological mother, Hikari, who is a sweet and thoughtful girl, portrayed by Aju Makita. Hikari hands them a heartfelt letter for her baby and expresses her sorrow over the situation.
As the story unfolds, a deeper flashback reveals Hikari's own dramatic tale. At just fourteen, she experiences her first love, which leads to an unexpected pregnancy. Due to her family's desire to protect her reputation and future, they send her to Baby Baton, where she finds solace among other expectant young women waiting to give birth.
Fast forward to the present, and Satoko receives another call from the kindergarten, bringing relief as the teacher confides that the other child has admitted to lying. The family, looking forward to a trip to the zoo, faces an unexpected twist when a woman claims to be Asato's mother, demanding that he be returned to her. This woman is revealed to be Hikari, who employs intimidation in her quest for money, threatening to expose their adoption when they express skepticism over her identity.
Struggling with her own feelings of displacement after leaving Baby Baton, Hikari seeks work there, only to learn of its impending closure. As she toils at the facility, Hikari stumbles upon records detailing her son’s adoptive parents, prompting her to move closer to them in the city. While delivering newspapers, she befriends a girl in a precarious situation with loan sharks, which ultimately leads to trouble as Hikari unwittingly becomes the victim of a forged signature.
As events take a turn, Hikari, driven by love, finally reaches out to her son’s adoptive parents. Hearing her son call for her makes her heart ache; despite the overwhelming emotion, she acknowledges her role and runs away, grasping her complex feelings of motherhood.
The climax unfolds when Satoko learns through the police about Hikari's true identity. Overcome with guilt for not recognizing her sooner, Satoko embarks on a journey to find Hikari, ultimately bringing her face to face with Asato, allowing for a profound and emotional reunion that encapsulates the film's themes of love, sacrifice, and identity.
