When his mother marries Kon Nishino, a divorced man whom she met at the hostess club, Rikutaro suddenly finds himself with a new father, as well as with a sister, Mariko.

Embarrassed, the children decide to engineer a divorce between Yayoi and Kon, to which purpose they sign a pact drawn up by Mariko.

First they try to persuade Kon that the marriage was a bad idea by spoiling the food and suggesting that the ghost of Rikutaro's father might be haunting the house.

Kon, who has found a job at a real estate agent, starts staying away until late at night, leaving the children to their own devices.

In the last scene, Kon packs up his car and drives away with Mariko, who is holding the lipstick Yayoi gave her and the piece of iron that she was given by Rikutaro.

The title refers to a scene in the film in which Takashi Iizuka tells Rikutaro that he, as a 'child of iron' is strong enough to pull through, in spite of the adversity.

Taking his own childhood experiences and those of his once-stepsister Mariko, Koki Fukuyama produced a basic script which he subsequently polished with professional writer Kaori Moriyama.

[5] In a February 2016 Q&A session, Koki Fukuyama stated that the film is about 'trying to survive and do one's best in situations that you really can't do anything about', both in the case of the children and their parents.