Through the hospital they are put in contact with the Saiki family, who own and live above a hardware store. Raised in a different social class, and under very different parenting tactics, the son of Yudai (Rirî Furankî) and Yukari (Yôko Maki), Ryusei (Shôgen Hwang), is very different to the kind, quiet nature of Keita. Not only has Yudai been a present and energetic influence on his growth, but Ryusei also has two younger siblings.
The families are encouraged to switch their children before elementary school, a mere six weeks away. They begin to spend time together and allow the boys to spend weekends at their respective houses in an attempt to acclimatise them into their future living arrangements. But, as expected, the decision is a difficult one, with parents and children individually affected by the unfortunate situation. Can they love a child without their blood the way they did before? Will Ryota choose his true biological son or the boy he has raised as his own?