Hiroto Komori (Yuya Yagira) works at city hall and leads a calm life, akin to a gentle breeze, alongside his younger brother Michito (Ryota Bando), who has autism spectrum disorder. After losing their parents early on, Hiroto has tailored his daily routine to match his brother’s, waking up, leaving the house, finishing work at city hall, and picking Michito up from his design company job—all at the same time each day. But one day, an unexpected visitor disrupts their peaceful life.

A boy (Tasuku Sato) suddenly appears before the brothers, introducing himself as “Lion.”

When Lion barges into their home, announcing he’ll “live here now,” Michito goes into a panic. In an attempt to return their lives to normal and protect his brother from change, Hiroto decides to have the boy taken into police custody. However, a mysterious message pops up on Lion’s phone: “I’ll leave the rest to you.” The text triggers a memory in Hiroto of someone he’d long forgotten. He soon notices bruises on Lion’s body, raising more questions.

Meanwhile, in a neighboring prefecture, Shogo Tachibana (Osamu Mukai) is frantically filing a missing persons report. Gradually, the case catches public attention as a “mother-child disappearance” incident.

Who left Lion here, and who is he? As Lion, who arrived like a storm, becomes a part of their lives, Hiroto and Michito’s bond begins to evolve. This human suspense drama unfolds, depicting the fierce love of people who will go to any lengths to protect those dear to them, even in the harshest of circumstances.