Saori Mugino, a devoted single mother, faces a troubling situation as she raises her fifth-grade son, Minato. His behavior takes a bizarre turn when he starts cutting his own hair and returns home with only one shoe. The situation escalates when one night, Minato goes missing, prompting Saori to frantically search for him. After making several calls, she ultimately finds him in an abandoned train tunnel.
Suspecting that Minato's teacher, Mr. Hori, might be abusing him, Saori approaches the school, only to be met with indifference from the faculty. The apathy peaks when Mr. Hori offers a surface-level apology that feels insincere. Upon confronting him directly, she learns that Minato may be bullying another student, Yori. This revelation leads her to visit Yori’s home, where she discovers that he, despite his own peculiarities, is both fond of and protective towards Minato.
In a shocking twist, Mr. Hori is dismissed from his teaching position but unexpectedly reappears shortly after. In a moment of tension, Minato falls down a flight of stairs while trying to evade him. Amidst a brewing storm, Hori visits Saori's home, only to realize that Minato has vanished yet again.
The narrative delves into Hori's perspective, revealing his suspicions about Minato's disruptive behavior, including troubling actions like throwing classmates' belongings and allegedly locking Yori in a bathroom stall. Hori's visit to Yori's home uncovers a challenging truth; Yori's father, Kiyotaka, struggles with alcoholism and delusion. As Saori presses for answers regarding Minato's welfare, Hori faces mounting pressure from the school staff to remain silent for the institution’s sake, leading to his resignation.
After facing media backlash and being abandoned by his girlfriend, Hori grapples with despair, considering a drastic step from the school rooftop after Minato's accident. In a moment of revelation during the storm, he discovers a typo in Yori's old homework that seems to hint at Minato's name. Realizing the connection, Hori rushes to apologize to Saori, only to find out Minato is still missing. Together, they return to the train tunnel, where they uncover an abandoned railcar partially submerged in mud, but tragically only find Minato’s discarded poncho inside.
The story circles back to Minato's perspective; he reflects on his bond with Yori, who faces bullying for his socially awkward demeanor. The two boys become inseparable as they find solace in their friendship, even as Minato grapples with burgeoning romantic feelings and his sense of inadequacy. One fateful night, they reach a breaking point after a tense encounter with Yori's father. In a turn of events during the storm, Minato discovers Yori abandoned in a bathtub, and together they seek refuge in their secret hideout within the abandoned railcar. As the rain clears, they emerge renewed, joyfully running through a field, hinting at a new beginning.
